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Daily Challenge #152 - Strongest Number in an Interval

thepracticaldev profile image dev.to staff ・1 min read

Daily Challenge (273 Part Series)

1) Daily Challenge #1 - String Peeler 2) Daily Challenge #2 - String Diamond 3 ... 271 3) Daily Challenge #3 - Vowel Counter 4) Daily Challenge #4 - Checkbook Balancing 5) Daily Challenge #5 - Ten Minute Walk 6) Daily Challenge #6 - Grandma and her friends 7) Daily Challenge #7 - Factorial Decomposition 8) Daily Challenge #8 - Scrabble Word Calculator 9) Daily Challenge #9 - What's Your Number? 10) Daily Challenge #10 - Calculator 11) Daily Challenge #11 - Cubic Numbers 12) Daily Challenge #12 - Next Larger Number 13) Daily Challenge #13 - Twice Linear 14) Daily Challenge #14 - Square into Squares 15) Daily Challenge #15 - Stop gninnipS My sdroW! 16) Daily Challenge #16 - Number of People on the Bus 17) Daily Challenge #17 - Double Trouble 18) Daily Challenge #18 - Triple Trouble 19) Daily Challenge #19 - Turn numbers into words 20) Daily Challenge Post #20 - Number Check 21) Daily Challenge #21 - Human Readable Time 22) Daily Challenge #22 - Simple Pig Latin 23) Daily Challenge #23 - Morse Code Decoder 24) Daily Challenge #24 - Shortest Step 25) Daily Challenge #25 - Double Cola 26) Daily Challenge #26 - Ranking Position 27) Daily Challenge #27 - Unlucky Days 28) Daily Challenge #28 - Kill the Monster! 29) Daily Challenge #29 - Xs and Os 30) Daily Challenge #30 - What is the price? 31) Daily Challenge #31 - Count IPv4 Addresses 32) Daily Challenge #32 - Hide Phone Numbers 33) Daily Challenge #33 - Did you mean...? 34) Daily Challenge #34 - WeIrD StRiNg CaSe 35) Daily Challenge #35 - Find the Outlier 36) Daily Challenge #36 - Let's go for a run! 37) Daily Challenge #37 - Name Swap 38) Daily Challenge #38 - Middle Name 39) Daily Challenge #39 - Virus 40) Daily Challenge #40 - Counting Sheep 41) Daily Challenge #41 - Greed is Good 42) Daily Challenge #42 - Caesar Cipher 43) Daily Challenge #43 - Boardgame Fight Resolver 44) Daily Challenge #44 - Mexican Wave 45) Daily Challenge #45 - Change Machine 46) Daily Challenge #46 - ??? 47) Daily Challenge #47 - Alphabets 48) Daily Challenge #48 - Facebook Likes 49) Daily Challenge #49 - Dollars and Cents 50) Daily Challenge #50 - Number Neighbor 51) Daily Challenge #51 - Valid Curly Braces 52) Daily Challenge #52 - Building a Pyramid 53) Daily Challenge #53 - Faro Shuffle 54) Daily Challenge #54 - What century is it? 55) Daily Challenge #55 - Building a Pile of Cubes 56) Daily Challenge #56 - Coffee Shop 57) Daily Challenge #57 - BMI Calculator 58) Daily Challenge #58 - Smelting Iron Ingots 59) Daily Challenge #59 - Snail Sort 60) Daily Challenge #60 - Find the Missing Letter 61) Daily Challenge #61 - Evolution Rate 62) Daily Challenge #62 - Josephus Survivor 63) Daily Challenge #63- Two Sum 64) Daily Challenge #64- Drying Potatoes 65) Daily Challenge #65- A Disguised Sequence 66) Daily Challenge #66- Friend List 67) Daily Challenge #67- Phone Directory 68) Daily Challenge #68 - Grade Book 69) Daily Challenge #69 - Going to the Cinema 70) Daily Challenge #70 - Pole Vault Competition Results 71) Daily Challenge #71 - See you next Happy Year 72) Daily Challenge #72 - Matrix Shift 73) Daily Challenge #73 - ATM Heist 74) Daily Challenge #74 - Free Pizza 75) Daily Challenge #75 - Set Alarm 76) Daily Challenge #76 - Bingo! (or not...) 77) Daily Challenge #77 - Bird Mountain 78) Daily Challenge #78 - Number of Proper Fractions with Denominator d 79) Daily Challenge #79 - Connect Four 80) Daily Challenge #80 - Longest Vowel Change 81) Daily Challenge #81 - Even or Odd 82) Daily Challenge #82 - English Beggars 83) Daily Challenge #83 - Deodorant Evaporator 84) Daily Challenge #84 - Third Angle of a Triangle 85) Daily Challenge #85 - Unwanted Dollars 86) Daily Challenge #86 - Wouldn't, not Would. 87) Daily Challenge #87 - Pony Express 88) Daily Challenge #88 - Recursive Ninjas 89) Daily Challenge #89 - Extract domain name from URL 90) Daily Challenge #90 - One Step at a Time 91) Daily Challenge #91 - Bananas 92) Daily Challenge #92 - Boggle Board 93) Daily Challenge #93 - Range Extraction 94) Daily Challenge #94 - Last Digit 95) Daily Challenge #95 - CamelCase Method 96) Daily Challenge #96 - Easter Egg Crush Test 97) Daily Challenge #97 - Greed is Good 98) Daily Challenge #98 - Make a Spiral 99) Daily Challenge #99 - Balance the Scales 100) Daily Challenge #100 - Round Up 101) Daily Challenge #101 - Parentheses Generator 102) Daily Challenge #102 - Pentabonacci 103) Daily Challenge #103 - Simple Symbols 104) Daily Challenge #104 - Matrixify 105) Daily Challenge #105 - High-Sum Matrix Drop 106) Daily Challenge #106 - Average Fuel Consumption 107) Daily Challenge #107 - Escape the Mines 108) Daily Challenge #108 - Find the Counterfeit Coin 109) Daily Challenge #109 - Decorate with Wallpaper 110) Daily Challenge #110 - Love VS. Friendship 111) Daily Challenge #111 - 99 Bottles of Beer 112) Daily Challenge #112 - Functions of Integers on the Cartesian Plane 113) Daily Challenge #113 - Iterative Rotation Cipher 114) Daily Challenge #114 - Speed Control 115) Daily Challenge #115 - Look and Say Sequence 116) Daily Challenge #116 - Shortest Knight Path 117) Daily Challenge #117 - MinMinMax 118) Daily Challenge #118 - Reversing a Process 119) Daily Challenge #119 - Adding Big Numbers 120) Daily Challenge #120 - Growth of a Population 121) Daily Challenge #121 - Who has the most money? 122) Daily Challenge #122 - Clockwise Spirals 123) Daily Challenge #123 - Curry me Softly 124) Daily Challenge #124 - Middle Me 125) Daily Challenge #125 - 23 Matches or More 126) Daily Challenge #126 - The Supermarket Line 127) Daily Challenge #127 - Playing with Passphrases 128) Daily Challenge #128 - Blackjack Scorer 129) Daily Challenge #129 - Clay Pigeon Shooting 130) Daily Challenge #130 - GCD Sum 131) Daily Challenge #131 - Remove Anchor from URL 132) Daily Challenge #132 - Is my friend cheating? 133) Daily Challenge #133 - Suitcase Packing 134) Daily Challenge #134 - Rice and Chessboard Problem 135) Daily Challenge #135 - The Wide Mouthed Frog! 136) Daily Challenge #136 - The Deaf Rats of Hamelin 137) Daily Challenge #137 - Help the Bookseller 138) Daily Challenge #138 - Do I get a Bonus? 139) Daily Challenge #138 - Keep Up the Hoop 140) Daily Challenge #140 - I love you, a little, a lot, passionately ... not at all 141) Daily Challenge #141 - Two Sum 142) Daily Challenge #142 - Parts of a Whole 143) Daily Challenge #143 - Big Arithmetic 144) Daily Challenge #144 - Box Office Clerk 145) Daily Challenge #145 - SET Card Game 146) Daily Challenge #146 - The Dollar Game 147) Daily Challenge #147 - NIM 148) Daily Challenge #148 - Disemvowel Trolls 149) Daily Challenge #149 - Fun with Lamps 150) Daily Challenge #150 - Boggle Guess Validator 151) Daily Challenge #151 - Reverse Parentheses 152) Daily Challenge #152 - Strongest Number in an Interval 153) Daily Challenge #153 - Horse Race Gamble 154) Daily Challenge #154 - Stable Arrangement 155) Daily Challenge #155 - Royal Arranged Marriages 156) Daily Challenge #162 - Taxi Dispatching 157) Daily Challenge #163 - Significant Figures 158) Daily Challenge #164 - Jump 159) Daily Challenge #165 - Password Lost in a Grid 160) Daily Challenge #166 - Cat and Mouse 161) Daily Challenge #167 - Return String As Sorted Blocks 162) Daily Challenge #168 - [Code golf] f (f (f b)) = f b 163) Daily Challenge #169 - Christmas Tree 164) Daily Challenge #170 - Pokemon Damage Calculator 165) Daily Challenge #171 - Ordering Beers in Poland 166) Daily Challenge #172 - Find All in an Array 167) Daily Challenge #173 - Pandemia 168) Daily Challenge #174 - Soccer League Table 169) Daily Challenge #175 - Complementary DNA 170) Daily Challenge #176 - Loopover 171) Daily Challenge #177 - Supersize Me 172) Daily Challenge #178 - Create Phone Numbers 173) Daily Challenge #179 - Hide Phone Numbers 174) Daily Challenge #180 - SMS Shortener 175) Daily Challenge #181 - Is King in Check? 176) Daily Challenge #182 - Arrh, grabscrab! 177) Daily Challenge #183 - Automorphic Numbers 178) Daily Challenge #184 - Form the Minimum 179) Daily Challenge #185 - House Numbers Sum 180) Daily Challenge #186 - Jumping Frog 181) Daily Challenge #187 - Most Sales 182) Daily Challenge #188 - Break camelCase 183) Daily Challenge #189 - Convert Number into Reversed Array 184) Daily Challenge #190 - capitalizeFirstLast 185) Daily Challenge #191 - Alphabetical Addition 186) Daily Challenge #192 - Can you Survive the Zombies? 187) Daily Challenge #193 - What's the Real Floor? 188) Daily Challenge #194 - Spread Number 189) Daily Challenge #195 - No Zeroes for Heroes 190) Daily Challenge #196 - Flou 191) Daily Challenge #197 - Population Growth 192) Daily Challenge #198 - 21 Blackjack 193) Daily Challenge #199 - List of All Rationals 194) Daily Challenge #200 - Longest Linear Palindromic Substring 195) Daily Challenge #201 - Complete the Pattern 196) Daily Challenge #202 - Complete the Pattern II 197) Daily Challenge #203 - Pascal's Triangle 198) Daily Challenge #204 - Partial Keys 199) Daily Challenge #205 - Consonant String Value 200) Daily Challenge #206 - Pound Means Backspace 201) Daily Challenge #207 - Snakes and Ladders 202) Daily Challenge #208 - Delete Occurrences of an Element 203) Daily Challenge #209 - Roman Numerals 204) Daily Challenge #210 - Separate Capitalization 205) Daily Challenge #211 - Product Partitions 206) Daily Challenge #212 - DNA to RNA 207) Daily Challenge #213 - Are they the "same"? 208) Daily Challenge #214 - Persistent Bugger 209) Daily Challenge #215 - Difference of 2 210) Daily Challenge #216 - Rainfall 211) Daily Challenge #217 - SMS w/ an Old Phone 212) Daily Challenge #218 - Possible Sides of a Non-Right Triangle 213) Daily Challenge #219 - Compare Strings 214) Daily Challenge #220 - What Dominates Your Array? 215) Daily Challenge #221 - The Merchant of York 216) Daily Challenge #222 - Parse Bank Account Numbers 217) Daily Challenge #223 - Responsible Drinking 218) Daily Challenge #224 - Password Validator 219) Daily Challenge #225 - Square'n'Sum 220) Daily Challenge #226 - Array to HTML Table 221) Daily Challenge #227 - Android Lock Screen 222) Daily Challenge #228 - Best Profit in Single Sale 223) Daily Challenge #229 - Haiku Validator 224) Daily Challenge #230 - Beeramid 225) Daily Challenge #231 - Perfect Powers 226) Daily Challenge #232 - Regex Pattern 227) Daily Challenge #233 - Get Planet Name by ID 228) Daily Challenge #234 - Happy Birthday! 229) Daily Challenge #235 - Reversing a Process 230) Daily Challenge #236 - RGB to Hex Conversion 231) Daily Challenge #237 - Delete Extra Occurrences 232) Daily Challenge #238 - One is the Loneliest Number 233) Daily Challenge #239 - Graceful Tipping 234) Daily Challenge #240 - ATM 235) Daily Challenge #241 - Tip Calculator 236) Daily Challenge #242 - Expressions Matter 237) Daily Challenge #243 - Redacted! 238) Daily Challenge #244 - Search for Letters 239) Daily Challenge #245 - Sort Santa's Reindeer 240) Daily Challenge #246 - Readable Specification Pattern 241) Daily Challenge #247 - Get Planet Name By ID 242) Daily Challenge #248 - Chinese Numerals 243) Daily Challenge #249 - Incremental Changes 244) Daily Challenge #250 - Last Digit of a Large Number 245) Daily Challenge #251 - Largest Number in a Sequence 246) Daily Challenge #252 - Everybody hates Mondays 247) Daily Challenge #253 - Sort Sentences Pseudo-alphabetically 248) Daily Challenge #254 - The Vowel Code 249) Daily Challenge #255 - Is There an Odd Bit? 250) Daily Challenge #256 - How Many Are Smaller Than I? 251) Daily Challenge #257 - Halving Sum 252) Daily Challenge #258 - Ranking Poker Hands 253) Daily Challenge #259 - Duplicate Encoder 254) Daily Challenge #260 - Subtract the Sum 255) Daily Challenge #261 - Diagonal Strings 256) Daily Challenge #262 - No One Likes Spare Change 257) Daily Challenge #263 - Reverse Words 258) Daily Challenge #264 - Digital Root 259) Daily Challenge #265 - Equal Sides 260) Daily Challenge #266 - Who Likes It? 261) Daily Challenge #267 - Braking Speed 262) Daily Challenge #268 - Swapping Characters in Strings 263) Daily Challenge #269 - Decompose n! 264) Daily Challenge #270 - Fix String Case 265) Daily Challenge #271 - Simulate Population Growth 266) Daily Challenge #272 - Printer Errors 267) Daily Challenge #273 - Remove Duplicates 268) Daily Challenge #274 - Aerial Firefighting 269) Daily Challenge #275 - Casino Chips 270) Daily Challenge #276 - Unwanted Dollar Signs 271) Daily Challenge #277 - Over the Road 272) Daily Challenge #278 - Find all non-consecutive numbers 273) Daily Challenge #279 - Playing with Sandpiles

Setup

The strength of an even number is determined by the amount of times we can successfully divide by 2 until we reach an odd number.

For example, if n = 12, then:
12 / 2 = 6
6 / 2 = 3
We have divided 12 in half twice and reached 3, so the strength of 12 is 2.

Given a closed interval [n, m], return the strongest even number in the interval. If multiple solutions exist, return the smallest of the possible solutions.

Examples

for [1, 2], return 2. (1 has a strenght of 0; 2 has a strength of 1)
for [5, 10], return 8.

Tests

[48, 56]
[129, 193]

Good luck~!


This challenge comes from alexmate on CodeWars. Thank you to CodeWars, who has licensed redistribution of this challenge under the 2-Clause BSD License!

Want to propose a challenge idea for a future post? Email yo+challenge@dev.to with your suggestions!

Daily Challenge (273 Part Series)

1) Daily Challenge #1 - String Peeler 2) Daily Challenge #2 - String Diamond 3 ... 271 3) Daily Challenge #3 - Vowel Counter 4) Daily Challenge #4 - Checkbook Balancing 5) Daily Challenge #5 - Ten Minute Walk 6) Daily Challenge #6 - Grandma and her friends 7) Daily Challenge #7 - Factorial Decomposition 8) Daily Challenge #8 - Scrabble Word Calculator 9) Daily Challenge #9 - What's Your Number? 10) Daily Challenge #10 - Calculator 11) Daily Challenge #11 - Cubic Numbers 12) Daily Challenge #12 - Next Larger Number 13) Daily Challenge #13 - Twice Linear 14) Daily Challenge #14 - Square into Squares 15) Daily Challenge #15 - Stop gninnipS My sdroW! 16) Daily Challenge #16 - Number of People on the Bus 17) Daily Challenge #17 - Double Trouble 18) Daily Challenge #18 - Triple Trouble 19) Daily Challenge #19 - Turn numbers into words 20) Daily Challenge Post #20 - Number Check 21) Daily Challenge #21 - Human Readable Time 22) Daily Challenge #22 - Simple Pig Latin 23) Daily Challenge #23 - Morse Code Decoder 24) Daily Challenge #24 - Shortest Step 25) Daily Challenge #25 - Double Cola 26) Daily Challenge #26 - Ranking Position 27) Daily Challenge #27 - Unlucky Days 28) Daily Challenge #28 - Kill the Monster! 29) Daily Challenge #29 - Xs and Os 30) Daily Challenge #30 - What is the price? 31) Daily Challenge #31 - Count IPv4 Addresses 32) Daily Challenge #32 - Hide Phone Numbers 33) Daily Challenge #33 - Did you mean...? 34) Daily Challenge #34 - WeIrD StRiNg CaSe 35) Daily Challenge #35 - Find the Outlier 36) Daily Challenge #36 - Let's go for a run! 37) Daily Challenge #37 - Name Swap 38) Daily Challenge #38 - Middle Name 39) Daily Challenge #39 - Virus 40) Daily Challenge #40 - Counting Sheep 41) Daily Challenge #41 - Greed is Good 42) Daily Challenge #42 - Caesar Cipher 43) Daily Challenge #43 - Boardgame Fight Resolver 44) Daily Challenge #44 - Mexican Wave 45) Daily Challenge #45 - Change Machine 46) Daily Challenge #46 - ??? 47) Daily Challenge #47 - Alphabets 48) Daily Challenge #48 - Facebook Likes 49) Daily Challenge #49 - Dollars and Cents 50) Daily Challenge #50 - Number Neighbor 51) Daily Challenge #51 - Valid Curly Braces 52) Daily Challenge #52 - Building a Pyramid 53) Daily Challenge #53 - Faro Shuffle 54) Daily Challenge #54 - What century is it? 55) Daily Challenge #55 - Building a Pile of Cubes 56) Daily Challenge #56 - Coffee Shop 57) Daily Challenge #57 - BMI Calculator 58) Daily Challenge #58 - Smelting Iron Ingots 59) Daily Challenge #59 - Snail Sort 60) Daily Challenge #60 - Find the Missing Letter 61) Daily Challenge #61 - Evolution Rate 62) Daily Challenge #62 - Josephus Survivor 63) Daily Challenge #63- Two Sum 64) Daily Challenge #64- Drying Potatoes 65) Daily Challenge #65- A Disguised Sequence 66) Daily Challenge #66- Friend List 67) Daily Challenge #67- Phone Directory 68) Daily Challenge #68 - Grade Book 69) Daily Challenge #69 - Going to the Cinema 70) Daily Challenge #70 - Pole Vault Competition Results 71) Daily Challenge #71 - See you next Happy Year 72) Daily Challenge #72 - Matrix Shift 73) Daily Challenge #73 - ATM Heist 74) Daily Challenge #74 - Free Pizza 75) Daily Challenge #75 - Set Alarm 76) Daily Challenge #76 - Bingo! (or not...) 77) Daily Challenge #77 - Bird Mountain 78) Daily Challenge #78 - Number of Proper Fractions with Denominator d 79) Daily Challenge #79 - Connect Four 80) Daily Challenge #80 - Longest Vowel Change 81) Daily Challenge #81 - Even or Odd 82) Daily Challenge #82 - English Beggars 83) Daily Challenge #83 - Deodorant Evaporator 84) Daily Challenge #84 - Third Angle of a Triangle 85) Daily Challenge #85 - Unwanted Dollars 86) Daily Challenge #86 - Wouldn't, not Would. 87) Daily Challenge #87 - Pony Express 88) Daily Challenge #88 - Recursive Ninjas 89) Daily Challenge #89 - Extract domain name from URL 90) Daily Challenge #90 - One Step at a Time 91) Daily Challenge #91 - Bananas 92) Daily Challenge #92 - Boggle Board 93) Daily Challenge #93 - Range Extraction 94) Daily Challenge #94 - Last Digit 95) Daily Challenge #95 - CamelCase Method 96) Daily Challenge #96 - Easter Egg Crush Test 97) Daily Challenge #97 - Greed is Good 98) Daily Challenge #98 - Make a Spiral 99) Daily Challenge #99 - Balance the Scales 100) Daily Challenge #100 - Round Up 101) Daily Challenge #101 - Parentheses Generator 102) Daily Challenge #102 - Pentabonacci 103) Daily Challenge #103 - Simple Symbols 104) Daily Challenge #104 - Matrixify 105) Daily Challenge #105 - High-Sum Matrix Drop 106) Daily Challenge #106 - Average Fuel Consumption 107) Daily Challenge #107 - Escape the Mines 108) Daily Challenge #108 - Find the Counterfeit Coin 109) Daily Challenge #109 - Decorate with Wallpaper 110) Daily Challenge #110 - Love VS. Friendship 111) Daily Challenge #111 - 99 Bottles of Beer 112) Daily Challenge #112 - Functions of Integers on the Cartesian Plane 113) Daily Challenge #113 - Iterative Rotation Cipher 114) Daily Challenge #114 - Speed Control 115) Daily Challenge #115 - Look and Say Sequence 116) Daily Challenge #116 - Shortest Knight Path 117) Daily Challenge #117 - MinMinMax 118) Daily Challenge #118 - Reversing a Process 119) Daily Challenge #119 - Adding Big Numbers 120) Daily Challenge #120 - Growth of a Population 121) Daily Challenge #121 - Who has the most money? 122) Daily Challenge #122 - Clockwise Spirals 123) Daily Challenge #123 - Curry me Softly 124) Daily Challenge #124 - Middle Me 125) Daily Challenge #125 - 23 Matches or More 126) Daily Challenge #126 - The Supermarket Line 127) Daily Challenge #127 - Playing with Passphrases 128) Daily Challenge #128 - Blackjack Scorer 129) Daily Challenge #129 - Clay Pigeon Shooting 130) Daily Challenge #130 - GCD Sum 131) Daily Challenge #131 - Remove Anchor from URL 132) Daily Challenge #132 - Is my friend cheating? 133) Daily Challenge #133 - Suitcase Packing 134) Daily Challenge #134 - Rice and Chessboard Problem 135) Daily Challenge #135 - The Wide Mouthed Frog! 136) Daily Challenge #136 - The Deaf Rats of Hamelin 137) Daily Challenge #137 - Help the Bookseller 138) Daily Challenge #138 - Do I get a Bonus? 139) Daily Challenge #138 - Keep Up the Hoop 140) Daily Challenge #140 - I love you, a little, a lot, passionately ... not at all 141) Daily Challenge #141 - Two Sum 142) Daily Challenge #142 - Parts of a Whole 143) Daily Challenge #143 - Big Arithmetic 144) Daily Challenge #144 - Box Office Clerk 145) Daily Challenge #145 - SET Card Game 146) Daily Challenge #146 - The Dollar Game 147) Daily Challenge #147 - NIM 148) Daily Challenge #148 - Disemvowel Trolls 149) Daily Challenge #149 - Fun with Lamps 150) Daily Challenge #150 - Boggle Guess Validator 151) Daily Challenge #151 - Reverse Parentheses 152) Daily Challenge #152 - Strongest Number in an Interval 153) Daily Challenge #153 - Horse Race Gamble 154) Daily Challenge #154 - Stable Arrangement 155) Daily Challenge #155 - Royal Arranged Marriages 156) Daily Challenge #162 - Taxi Dispatching 157) Daily Challenge #163 - Significant Figures 158) Daily Challenge #164 - Jump 159) Daily Challenge #165 - Password Lost in a Grid 160) Daily Challenge #166 - Cat and Mouse 161) Daily Challenge #167 - Return String As Sorted Blocks 162) Daily Challenge #168 - [Code golf] f (f (f b)) = f b 163) Daily Challenge #169 - Christmas Tree 164) Daily Challenge #170 - Pokemon Damage Calculator 165) Daily Challenge #171 - Ordering Beers in Poland 166) Daily Challenge #172 - Find All in an Array 167) Daily Challenge #173 - Pandemia 168) Daily Challenge #174 - Soccer League Table 169) Daily Challenge #175 - Complementary DNA 170) Daily Challenge #176 - Loopover 171) Daily Challenge #177 - Supersize Me 172) Daily Challenge #178 - Create Phone Numbers 173) Daily Challenge #179 - Hide Phone Numbers 174) Daily Challenge #180 - SMS Shortener 175) Daily Challenge #181 - Is King in Check? 176) Daily Challenge #182 - Arrh, grabscrab! 177) Daily Challenge #183 - Automorphic Numbers 178) Daily Challenge #184 - Form the Minimum 179) Daily Challenge #185 - House Numbers Sum 180) Daily Challenge #186 - Jumping Frog 181) Daily Challenge #187 - Most Sales 182) Daily Challenge #188 - Break camelCase 183) Daily Challenge #189 - Convert Number into Reversed Array 184) Daily Challenge #190 - capitalizeFirstLast 185) Daily Challenge #191 - Alphabetical Addition 186) Daily Challenge #192 - Can you Survive the Zombies? 187) Daily Challenge #193 - What's the Real Floor? 188) Daily Challenge #194 - Spread Number 189) Daily Challenge #195 - No Zeroes for Heroes 190) Daily Challenge #196 - Flou 191) Daily Challenge #197 - Population Growth 192) Daily Challenge #198 - 21 Blackjack 193) Daily Challenge #199 - List of All Rationals 194) Daily Challenge #200 - Longest Linear Palindromic Substring 195) Daily Challenge #201 - Complete the Pattern 196) Daily Challenge #202 - Complete the Pattern II 197) Daily Challenge #203 - Pascal's Triangle 198) Daily Challenge #204 - Partial Keys 199) Daily Challenge #205 - Consonant String Value 200) Daily Challenge #206 - Pound Means Backspace 201) Daily Challenge #207 - Snakes and Ladders 202) Daily Challenge #208 - Delete Occurrences of an Element 203) Daily Challenge #209 - Roman Numerals 204) Daily Challenge #210 - Separate Capitalization 205) Daily Challenge #211 - Product Partitions 206) Daily Challenge #212 - DNA to RNA 207) Daily Challenge #213 - Are they the "same"? 208) Daily Challenge #214 - Persistent Bugger 209) Daily Challenge #215 - Difference of 2 210) Daily Challenge #216 - Rainfall 211) Daily Challenge #217 - SMS w/ an Old Phone 212) Daily Challenge #218 - Possible Sides of a Non-Right Triangle 213) Daily Challenge #219 - Compare Strings 214) Daily Challenge #220 - What Dominates Your Array? 215) Daily Challenge #221 - The Merchant of York 216) Daily Challenge #222 - Parse Bank Account Numbers 217) Daily Challenge #223 - Responsible Drinking 218) Daily Challenge #224 - Password Validator 219) Daily Challenge #225 - Square'n'Sum 220) Daily Challenge #226 - Array to HTML Table 221) Daily Challenge #227 - Android Lock Screen 222) Daily Challenge #228 - Best Profit in Single Sale 223) Daily Challenge #229 - Haiku Validator 224) Daily Challenge #230 - Beeramid 225) Daily Challenge #231 - Perfect Powers 226) Daily Challenge #232 - Regex Pattern 227) Daily Challenge #233 - Get Planet Name by ID 228) Daily Challenge #234 - Happy Birthday! 229) Daily Challenge #235 - Reversing a Process 230) Daily Challenge #236 - RGB to Hex Conversion 231) Daily Challenge #237 - Delete Extra Occurrences 232) Daily Challenge #238 - One is the Loneliest Number 233) Daily Challenge #239 - Graceful Tipping 234) Daily Challenge #240 - ATM 235) Daily Challenge #241 - Tip Calculator 236) Daily Challenge #242 - Expressions Matter 237) Daily Challenge #243 - Redacted! 238) Daily Challenge #244 - Search for Letters 239) Daily Challenge #245 - Sort Santa's Reindeer 240) Daily Challenge #246 - Readable Specification Pattern 241) Daily Challenge #247 - Get Planet Name By ID 242) Daily Challenge #248 - Chinese Numerals 243) Daily Challenge #249 - Incremental Changes 244) Daily Challenge #250 - Last Digit of a Large Number 245) Daily Challenge #251 - Largest Number in a Sequence 246) Daily Challenge #252 - Everybody hates Mondays 247) Daily Challenge #253 - Sort Sentences Pseudo-alphabetically 248) Daily Challenge #254 - The Vowel Code 249) Daily Challenge #255 - Is There an Odd Bit? 250) Daily Challenge #256 - How Many Are Smaller Than I? 251) Daily Challenge #257 - Halving Sum 252) Daily Challenge #258 - Ranking Poker Hands 253) Daily Challenge #259 - Duplicate Encoder 254) Daily Challenge #260 - Subtract the Sum 255) Daily Challenge #261 - Diagonal Strings 256) Daily Challenge #262 - No One Likes Spare Change 257) Daily Challenge #263 - Reverse Words 258) Daily Challenge #264 - Digital Root 259) Daily Challenge #265 - Equal Sides 260) Daily Challenge #266 - Who Likes It? 261) Daily Challenge #267 - Braking Speed 262) Daily Challenge #268 - Swapping Characters in Strings 263) Daily Challenge #269 - Decompose n! 264) Daily Challenge #270 - Fix String Case 265) Daily Challenge #271 - Simulate Population Growth 266) Daily Challenge #272 - Printer Errors 267) Daily Challenge #273 - Remove Duplicates 268) Daily Challenge #274 - Aerial Firefighting 269) Daily Challenge #275 - Casino Chips 270) Daily Challenge #276 - Unwanted Dollar Signs 271) Daily Challenge #277 - Over the Road 272) Daily Challenge #278 - Find all non-consecutive numbers 273) Daily Challenge #279 - Playing with Sandpiles

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Discussion

markdown guide
 

One way to be sneaky about solving this problem comes from realizing what the problem is asking for when it says to "divide by 2 until we reach an odd number." If you think about the binary representation of an integer, there's only one way for it to be odd - that is, for its lowest/least-significant bit to be set to 1. Also recalling that dividing by two is equivalent to a single bitshift to the right, we can find a neat trick.

With 12 as an example, we can see that in binary it is 1100, so it would take two bitshifts right for it to be odd - that is, to turn it into 11 (3). So we don't need to actually divide 12 until we get 3, but simply count the number of trailing zeroes in 12 and use that as its strength - which would be 2, in this case. From there, we just need to keep track of the largest-strength-with-smallest-number combo and we'll be fine. With all that said, here's that strategy implemented in Python:

#!/usr/bin/env python3


def trailing_zeroes(num):
    num_trailing = 0
    while num & 1 == 0:
        # loop/bitshift right until we find a nonzero bit
        num_trailing += 1
        num = num >> 1
    return num_trailing


def find_strongest(start, stop):
    """Return the strongest number in a closed interval as per dev.to challenge #152
    """
    max_strength = 0
    best_num = 0
    # add 1 to halt the loop at the value of stop, not stop - 1
    for i in range(start, stop + 1):
        if i % 2 == 1:
            # don't bother with odd numbers
            continue
        # the strength given in the spec can be expressed
        # as the number of trailing zeroes in the number
        strength = trailing_zeroes(i)
        if strength > max_strength:
            max_strength = strength
            best_num = i
        elif strength == max_strength:
            # as per the spec, choose the lower number
            best_num = min(best_num, i)
    return best_num


if __name__ == "__main__":
    print(find_strongest(1, 2))
    print(find_strongest(5, 10))
    print(find_strongest(48, 56))
    print(find_strongest(129, 193))

edit/take #2: I tried to think about a way to optimize the trailing zero calculation for a while, but couldn't come up with anything; so I gave up and decided to search around a little bit to find if anyone came up with an O(1) method to calculate the trailing-zero problem instead of the naive linear solution I posted. Turns out someone did, and the link can probably explain better than I. The result of integrating that solution with the code I posted earlier is below:

#!/usr/bin/env python3


# the below function is adapted from https://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightModLookup
def trailing_zeroes_fast(num):
    lookup = [32, 0, 1, 26, 2, 23, 27, 0, 3, 16, 24, 30,
              28, 11, 0, 13, 4, 7, 17, 0, 25, 22, 31, 15,
              29, 10, 12, 6, 0, 21, 14, 9, 5, 20, 8, 19, 18]
    num_trailing = lookup[(-num & num) % 37]
    return num_trailing


def find_strongest(start, stop):
    """Return the strongest number in a closed interval as per dev.to challenge #152
    """
    max_strength = 0
    best_num = 0
    # add 1 to halt the loop at the value of stop, not stop - 1
    for i in range(start, stop + 1):
        if i % 2 == 1:
            # don't bother with odd numbers
            continue
        # the strength given in the spec can be expressed
        # as the number of trailing zeroes in the number
        strength = trailing_zeroes_fast(i)
        if strength > max_strength:
            max_strength = strength
            best_num = i
        elif strength == max_strength:
            # as per the spec, choose the lower number
            best_num = min(best_num, i)
    return best_num


if __name__ == "__main__":
    print(find_strongest(1, 2))
    print(find_strongest(5, 10))
    print(find_strongest(48, 56))
    print(find_strongest(129, 193))

As a sidenote, an alternative method to count trailing zeroes to is to use the base 2 log of (-num & num), i.e, math.log2(num & -num) - in essence, this is asking how many bitshifts left starting from 1 are needed to hit the first set bit of num - but while it's clearly shorter and definitely more understandable, I don't believe this is faster than the lookup table route.

 

The optimization of using bit operations to find the "strength" of a number is a low hanging fruit, but the relationship between the number's strength and its binary representation can be taken much farther than that - to the point of solving this in logarithmic(!) time:

fn strongest_number(min: usize, max: usize) -> usize {
    assert!(min <= max);
    if min == max {
        // Otherwise the second `while` loop will not end
        return min;
    }
    let mut prefix_mask = !0usize;
    while 0 != (prefix_mask & max) {
        prefix_mask <<= 1;
    }
    while (prefix_mask & max) == (prefix_mask & min) {
        prefix_mask |= prefix_mask >> 1;
    }
    if (prefix_mask & min) == min {
        min
    } else {
        prefix_mask & max
    }
}

fn main() {
    assert_eq!(strongest_number(1, 2), 2);
    assert_eq!(strongest_number(5, 10), 8);
    assert_eq!(strongest_number(48, 56), 48);
    assert_eq!(strongest_number(129, 193), 192);
}

Explanation:

You can compare two numbers, padded to the same length, by finding their longest common prefix and then looking at the highest digit that's different. This work in any base, but farther ahead we'll use some properties unique to binary so let's stick with that.

For example, if we take 129 and 193 and convert them to binary:

129: 0000000010000001
193: 0000000011000001

We can see that both start with 000000001, and then 129 has 0000001 while 193 has 1000001. So the highest nonshared digit is 0 for 129 and 1 for 193 - which is why 193 is higher (yup - that's the direction the causation works here. Though this is math, so one can twist it to be the other way around...)

Lemma: Any number between the lower and higher bounds will share that same prefix with them.
Proof: If it doesn't, then at least one digit is different. Take the most significant digit where the number is different than the shared prefix. If it's 0 for the number and 1 for the prefix - this means the number is lower than the lower bound. If it's 1 for the number and 0 for the prefix - this means the number is higher than the higher bound.

So, the strongest number, being in the range, must also have that prefix. The strongest number with that prefix is just the prefix with only zeroes after it (remember - the number of digits is fixed!). That's also the lowest number in that range, so if it's equal to the lower bound - that's the strongest number in the range. Otherwise - the next strongest number is the prefix, a single one after it, and after that only zeroes. This number is guaranteed to not be higher than the higher bound, because they share the original common prefix plus a single one after it - and that number is the lowest in that prefix, since after that it's all zeroes.

 

That is just so clean, well thought and well explained! Congrats!

 

Some JS oneliners!

g=n=>(n>>>0).toString(2).split`1`.pop().length

f=n=>{i=n[0],m=0;while(i<=n[1]){m=Math.max(m,g(i));++i}return m}

The g method takes a number, converts it to binary, and return the number of trailing zeroes. Then, the f method loops through the input interval in order to return the maximum power

 

Don't write functions that already exist...

let strongestIn (n:int) (m:int) =
    seq {n..m} |> Seq.maxBy BitOperations.TrailingZeroCount

(F#)

 

Available since .NET Core 3.0 ... nice touch! Also in F# the Sequence generation is SO MUCH easier.
In C# you'd be better off with a simple for-loop.

public static long StrongestNumber(long start, long end)
{
   long strongestNum = 0;
   int bitCount = -1;
   for (long i = start; i<=end; ++i)
   {
       int currentBitCount = BitOperations.TrailingZeroCount(i);
       if (currentBitCount > bitCount)
       {
           bitCount = currentBitCount;
           strongestNum = i;
       }
   }
   return strongestNum;
}
 

Well, my F# solution translated to C# would be something like this;

static int StrongestIn(int n, int m)
{
    return Enumerable.Range(n, (m-n))
        .Aggregate((a,b) => BitOperations.TrailingZeroCount(a) > BitOperations.TrailingZeroCount(b)
            ? a : b);
}

There is no built in "MaxBy" in the C#, so here I replaced it with an Aggregate. (The TrailingZeroCount method will use intrinsics (e.g. a CPU instruction) if its available, so I'm not worried about calling it repeatedly for the accumulator.)

 

Hello guys, this is my first time here, and this is my recursive approach:

function strongest(from, to, times = 0) {
    if (from > to) return false;
    if (to - from < 1) return from * (2 ** times);
    if (to - from < 2) return (from + (from % 2)) * (2 ** times);
    return strongest((from + (from % 2)) / 2, (to - (to % 2)) / 2, times + 1);
}

EDIT without times:

function strongest(from, to) {
    if (from > to) return false;
    if (to - from < 1) return from;
    if (to - from < 2) return from + (from % 2);
    return 2 * strongest((from + (from % 2)) / 2, (to - (to % 2)) / 2);
}
 

Not the most efficient answer, but it is!


const findStrongestNumber = () => {
 let interval = [
   parseInt(document.querySelector("#num1").value),
   parseInt(document.querySelector("#num2").value)
 ];

  let numStrength = [0, 0];

  for(let i = 0; i < interval.length; i++) {
    let num = interval[i];

    while ((num % 2) !== 1) {
      num/=2;
      numStrength[i]++;
    }
  }

  let answer = 0;
  if(numStrength[0] > numStrength[1]) {
    answer = interval[0];
  } else if (numStrength[1] > numStrength[0]) {
    answer = interval[1]
  } else {
    if(interval[0] < interval[1]) {
      answer = interval[0];
    } else {
      answer = interval[1];
    }
  }

  document.querySelector("#answer").innerHTML = answer;
}

CodePen

 

Haskell

strongest :: (Int, Int) -> (Int, Int) -> (Int, Int)
strongest (strongestIndex, strongestValue) (index, value)
    | value > strongestValue = (index, value)
    | value == strongestValue && index < strongestIndex = (index, value)
    | otherwise = (strongestIndex, strongestValue)


strength :: Int -> Int
strength 0 = 0
strength number 
    | odd number = 0
    | otherwise = 1 + strength (div number 2)


strongestBetween :: Int -> Int -> Int
strongestBetween lowerbound upperbound =
    fst $ foldl1 strongest $ zip interval $ map strength interval

    where
        interval :: [Int]
        interval =
            [lowerbound..upperbound]


main :: IO ()
main = do
    print $ strongestBetween 1 2        -- 2
    print $ strongestBetween 5 10       -- 8
    print $ strongestBetween 48 56      -- 48
    print $ strongestBetween 129 193    -- 192

Try it.

 

Inefficient Python w/ tail recursion:

def strongness_tail(n, a):
    return a if n % 2 == 1 else strongness_tail(n/2, 1 + a)

def strongness(n):
    return strongness_tail(n, 0)

def strongest_even(n, m):
    strongest = [-1, -1]
    for i in range(n, m+1):
        strength = strongness(i)
        if strength > strongest[0]:
            strongest = [strength, i]

    return strongest[1]
 

In Go.

func strongest(start, stop int) int {
    power := func(num int) int {
        numSlice := strings.Split(fmt.Sprintf("%b", num), "1")
        return len(numSlice[len(numSlice)-1])
    }

    hp := 0
    var result int

    for i := start; i <= stop; i++ {
        if hp < power(i) {
            hp = power(i)
            result = i
        }
    }

    return result
}
 

Probably not a very efficient way to do it, but it works:

def strongest_number(interval):
  counter = interval[0]
  numbers = []
  while counter <= interval[1]:
    if counter % 2 == 0: numbers.append(counter) 
    counter += 1
  strengths = {}
  for i in range(len(numbers)):
    result = numbers[i]
    count = 0
    while result % 2 == 0:
      result = result / 2
      count += 1
    strengths[i] = count
  largest = 0
  k = ""
  for key in strengths:
    if strengths[key] > largest:
      largest = strengths[key]
      k = key
  return numbers[k]

 
const calcMaxStrength = (numbers) => {
  const divider = 2;

  const isOdd = number => number % 2 === 0;

  const calcStrength = (dividend, strength = 0) => {
    if (isOdd(dividend)) {
      return calcStrength(dividend / divider, strength += 1);
    }

    return strength;
  };

  return Math.max(...numbers.map(number => calcStrength(number)));
};

console.log(calcMaxStrength([48, 56])); // 4
console.log(calcMaxStrength([129, 193])); // 0
 

Here's a Nim submission!

proc even(i: int): bool {.inline.} = i mod 2 == 0

proc numStrength(i: int): int =
  ## Calculate the strength of a number.
  ##
  ## A number's strength is determined by the number of times
  ## it can divided in half until it reaches an odd number.
  var i = i
  while i.even:
    i = i div 2
    inc(result)

proc strongestNum(n, m: int): int =
  ## Given the closed interval [n, m], calculate the strongest number.
  var topStrength = 0
  for i in n..m:
    let strength = numStrength(i)
    if strength > topStrength:
      topStrength = strength
      result = i

assert strongestNum(1, 2) == 2
assert strongestNum(5, 10) == 8
assert strongestNum(48, 56) == 48
assert strongestNum(129, 193 == 192

There's definitely room to improve this, but I'm just starting to look into Nim's standard library, and I don't know all that's available to me yet.

 

Did it long hand in js. Great puzzle!

const strength = num => {
  let count = 0;
  if (num === 0) {
    return 0;
  }
  while (num % 2 == 0) {
    num = num / 2;
    count++;
  }
  return count;
};

const strongestNumber = interval => {
  const [start, end] = interval;
  let strongest = start;

  for (let i = start; i <= end; i++) {
    if (strength(i) > strength(strongest)) {
      strongest = i;
    }
  }
  return strongest;
};

console.log(strongestNumber([1, 2]));
console.log(strongestNumber([5, 10]));
console.log(strongestNumber([48, 56]));
console.log(strongestNumber([129, 193]));
 

Ruby

def get_strength(num)
  strength=0
  while !num.odd?
      num /= 2
      strength += 1
  end
  strength
end

def get_num_of_lowest_strength(nums)
  strength=Array.new
  nums.each do 
    |x| 
    strength.push [x, get_strength(x)]
  end  
  strength.sort_by{|k,v| [v,k]}.reverse
end

nums=[5..10,48..56,129..193]

nums.each do
  |num|
  x= get_num_of_lowest_strength(num)
  p x[0][0]
end
 

Raku:

sub strongest($a, $b) { 
  max($a..$b, :by({$_.lsb})) 
}

See it in action:

> strongest(1,2);
2
> strongest(5,10);
8
> strongest(48, 56);
48
> strongest(129,193);
192