Intro 🌐
Problem solving is an important skill, for your career and your life in general.
That's why I take interesting katas of all levels, customize them and explain how to solve them.
Understanding the Exercise❗
First, we need to understand the exercise!
If you don't understand it, you can't solve it!.
My personal method:
- Input: What do I put in?
- Output: What do I want to get out?
Today's exercise
Today, another 7 kyu kata,
meaning we slightly increase the difficulty.
Source: Codewars
Write a function missingValues, that accepts one parameter: myArray.
Given an array of number, e.g. [1, 1, 1, 2, 2, 3],
find:
- the number
x, that appears once, e.g.3 - the number
y, that appears twice, e.g.2
and return the product x * x * y, e.g. 18 (=> 3 x 3 x 2).
Input: an array of numbers.
Output: a number.
Thinking about the Solution 💭
I think I understand the exercise (= what I put into the function and what I want to get out of it).
Now, I need the specific steps to get from input to output.
I try to do this in small baby steps:
- Find the number that appears once,
x - Find the number that appears twice,
y - Return the product of
x * x * y
Example:
- Input:
[1, 1, 1, 2, 2, 3] - Find the number that appears once,
x:3 - Find the number that appears twice,
y:2 - Return the product of
x * x * y:18(=>3 x 3 x 2) - Output:
18✅
Implementation ⛑
function missingValues(myArray) {
// count amount of each number
const count = myArray.reduce(
(acc, cur) =>
acc.hasOwnProperty(cur)
? { ...acc, [cur]: acc[cur] + 1 }
: { ...acc, [cur]: 1 },
{}
);
// helper function to find the object key (= our number) that appears [amount] times
const appears = (amount) =>
Object.entries(count)
.filter(([key, value]) => value === amount)
.map((entry) => entry[0]);
return appears(1) * appears(1) * appears(2);
}
Result
console.log([1, 1, 1, 2, 2, 3]);
// 18 ✅
console.log([6, 5, 4, 100, 6, 5, 4, 100, 6, 5, 4, 200]);
// 4000000 ✅
Playground ⚽
You can play around with the code here
Next Part ➡️
Great work!
We learned how to use reduce, filter, map, hasOwnProperty, Object.entries.
I hope you can use your new learnings to solve problems more easily!
Next time, we'll solve another interesting kata. Stay tuned!
If I should solve a specific kata, shoot me a message here.
If you want to read my latest stuff, get in touch with me!
Further Reading 📖
Questions ❔
- How often do you do katas?
- Which implementation do you like more? Why?
- Any alternative solution?
Top comments (1)
This doesn't look like a very reasonable use of reduce.
I'd suggest starting with something like this.