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Daily Challenge #47 - Alphabets

thepracticaldev profile image dev.to staff ・1 min read

In today's challenge, you are asked to replace every letter with its position in the alphabet for a given string where 'a' = 1, 'b'= 2, etc.

For example:

alphabet_position("The sunset sets at twelve o' clock.") should return 20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11 as a string.


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

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

Discussion

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aminnairi profile image
Amin

JavaScript

My take at the challenge in JavaScript.

Source-Code

"use strict";

function lettersOnly(letterOrElse) {
  return letterOrElse.toUpperCase() !== letterOrElse.toLowerCase();
}

function toAlphabetPosition(letter) {
  return letter.toLowerCase().charCodeAt(0) - 'a'.charCodeAt(0) + 1;
}

function alphabet_position(input) {
  return Array
    .from(input)
    .filter(lettersOnly)
    .map(toAlphabetPosition)
    .join(" ");
}

const result = alphabet_position("The sunset sets at twelve o' clock.");
const expectations = "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11";

assert(result === expectations); // undefined (meaning OK)

Test it yourself

Available online here.

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jasman7799 profile image
Jarod Smith

love how readable this is

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aminnairi profile image
Amin

Thank you sir!

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jasman7799 profile image
Jarod Smith
const alphaPosition = str => [...str]
  .filter(letter => letter.toLowerCase().charCodeAt(0) - 96 > 0)
  .map(letter => letter.toLowerCase().charCodeAt(0) - 96)
  .reduce((s, pos) => s += `${pos} `, '')
  .trim();

classic map filter reduce problem loved it.

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serbuvlad profile image
Șerbu Vlad Gabriel

x86_64 assembly (System V ABI, GNU assembler), as usual. Not really correct, since there will be an extra ' ' at the end which I was too lazy to remove, but it'll do.

alphabetic_position.S

    .global alphabetic_position

    .text
alphabetic_position:
    #using these registers to avoid sprintf breaking them
    push %rbx
    push %rbp

    mov %rdi, %rbx
    mov %rdi, %r12
    mov %rsi, %rbp

    xor %eax, %eax
    xor %edx, %edx
loop:
    mov (%rbp), %dl

    cmp $65, %dl # 'A'
    jl skip

    cmp $91, %dl # 'Z' + 1
    jl print

    cmp $97, %dl # 'a'
    jl skip

    cmp $123, %dl # 'z' + 1
    ja skip

printl:
    sub $32, %dl # 'a' -> 'A'
print:
    sub $64, %dl # 'A' -> 1

    push %rdx

    mov %rbx, %rdi
    mov $format, %rsi
    call sprintf

    add %rax, %rbx

    pop %rdx
skip:
    inc %rbp
    cmp $0, %dl
    jne loop

    mov %r12, %rax

    pop %rbp
    pop %rbx
    ret


    .section .rodata
format:
    .asciz "%d "

alphabetic_position.h:

char *alphabetic_position(char *dst, const char *src);

Edit: the function name now conforms to the specification, as well as with the "returns the string" requirement (by returning a copy of dst).

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hectorpascual profile image
Héctor Pascual

that's crazy

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tiash990 profile image
Tiash

In C++

#include <string>
#include <iostream>

void alphabet_position(std::string s) {
    for (int i = 0; i < s.size(); i++)
    {
        int pos = (int)((char)s[i] - 'a');
        pos = pos < 0 ? pos + ('a' - 'A') : pos;
        if (pos >= 0 && pos <= 'z' - 'a') {
            std::cout << pos+1 << " ";
        }
    }
}

int main (int argc, char *argv[])
{
    alphabet_position("<The quick brown fox jumps over the lazy dog!>");
    //print 20 8 5 17 21 9 3 11 2 18 15 23 14 6 15 24 10 21 13 16 19 15 22 5 18 20 8 5 12 1 26 25 4 15 7
    return 0;
}

Edited: there was a bug :D

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aadibajpai profile image
Aadi Bajpai

Python one liner to the rescue 🙂

print(*[ord(x.lower())-96 for x in input() if x.isalpha()])

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brightone profile image
Oleksii Filonenko

Rust:

pub fn alphabet_position(text: &str) -> String {
    text.to_lowercase()
        .chars()
        .filter(|c| c.is_alphabetic())
        .map(|char| (char as usize - 96).to_string())
        .collect::<Vec<String>>()
        .join(" ")
}

#[test]                                                                                        
fn test_alphabet_position() {                                                                  
    assert_eq!(                                                                                
        alphabet_position("The sunset sets at twelve o' clock."),                              
        String::from("20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11")
    );                                                                                         
}                                                                                              
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jasman7799 profile image
Jarod Smith

this has shown me how similar rust syntax can be to JavaScript syntax wow

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alvaromontoro profile image
Alvaro Montoro

JavaScript

const code = s => [...s].reduce((a, v) => v.match(/[a-z]{1}/i) 
                                          ? a+(v.toLowerCase().charCodeAt(0)-96)+' ' 
                                          : a
                        , '')
                        .trim();

And as an extra, the decoder:

const decode = s => String.fromCharCode(...s.split(' ').map(val=>parseInt(val) + 96));

Although the decoding process is not perfect, because all the spaces and symbols are lost during the coding process. For example, the sentence "The sunset sets at twelve o' clock" will be coded into:

"20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11"

Which will be decoded into:

"thesunsetsetsattwelveoclock"

Link to live demo.

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craigmc08 profile image
Craig McIlwrath
import Data.Maybe (catMaybes)
import Data.List (find)
import Data.Functor (fmap)
import Data.Char (toLower) 

alpha = ['a'..'z']

isAlpha :: Char -> Bool
isAlpha = (`elem` alpha)

(>.<) :: (a -> b -> d) -> (c -> b) -> (a -> c -> d)
a >.< b = flip $ flip a . b

toNumber :: Char -> Maybe Int
toNumber = fmap snd . (flip find) alphaNum . ((==) >.< fst)
  where alphaNum = zip alpha [1..]

encodeMsg :: String -> String
encodeMsg = unwords . map show . catMaybes . map toNumber . filter isAlpha . map toLower

I wanted to try to write this function completely using point-free style. It led to me having to write that >.< operator, which you can see from the type definition exactly what it does. It was a good mental exercise in types for me, a Haskell beginner.

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curtisfenner profile image
Curtis Fenner

You don't need your filter isAlpha and isAlpha functions, since toNumber already returns None when the character isn't a letter, which chops off a nice bit of the solution!

You can also use findIndex from Data.List instead of find-with-zip (though that solution is cool! 😋

toNumber = (fmap (+1)) . (flip findIndex alpha) . (==)
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suchafoka profile image
Suchafoka

Python

import string
def alphabet_position(text):
    text = [i for i in text.replace(' ','').lower() if i.isalpha() ]
    position = [str(string.ascii_lowercase.find(i)+1) for i in text ]
    return ' '.join(position)
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peter279k profile image
peter279k

Here is the simple solution with PHP:

function alphabet_position(string $s): string {
    $s = strtoupper($s);
    $alphabetNums = range(65, 90);
    $alphabets = [];

    foreach ($alphabetNums as $chr) {
        $aphabets[] = chr($chr);
    }

    $result = "";

    $index = 0;
    for (; $index < strlen($s); $index++) {
        if (in_array($s[$index], $aphabets) === false) {
            continue;
        }

        $result .= (string)(ord($s[$index]) - 64) . " ";
    }

    return substr($result, 0, -1);
}
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avalander profile image
Avalander

Haskell

Some function composition sorcery in Haskell.

import Data.Char (isLetter, toUpper, ord)

alphabet_position :: String -> String
alphabet_position = unwords . map (show . (flip (-)) 64 . ord . toUpper) . filter isLetter

Explanation

The . operator composes functions, so they will be applied from right to left.

  1. filter isLetter will remove all characters that are not letters from the string.
  2. map (show . (flip (-)) 64 . ord . toUpper) Transforms each character to its position in the alphabet.
    1. toUpper transforms the character to uppercase, so that we can substract 64 from it's code to know the position.
    2. ord maps a character to its ASCII code.
    3. (flip (-) 64) subtracts 64 from the character code. Since the code for 'A' is 65, this will give us the position in the alphabet starting at index 1. The way it works is it partially applies the second argument of the subtract operator to 64, i.e., this is equivalent to (\x -> x - 64) but fancier.
    4. show maps any type deriving from Show (Int in this case) to String.
  3. unwords joins a list of strings using space as a separator.
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celyes profile image
Ilyes Chouia

a bit late but here's the answer anyway... in PHP

function alphabet_position($text){
    $alphabet = range('a', 'z');     
    $strippedText = str_split(strtolower(preg_replace("/[^a-zA-Z]/", "", $text)));   
    $result = "";
    foreach($strippedText as $letter){
        $result .= array_search($letter, $alphabet)+1 . " ";   
    }
    return $result;
}
echo alphabet_position("The sunset sets at twelve o' clock.");
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curtisfenner profile image
Curtis Fenner

Lua, just as a series of string operations:

local function solution(text)
    return text:lower()
        :gsub("%A+", "")
        :gsub("%a", function(n) return " " .. 1 + n:byte() - string.byte("a") end)
        :sub(2)
end

Lua, written with a loop and so a bit less wasteful:

local function solution(text)
    local ns = {}
    for a in text:gmatch("%a") do
        table.insert(ns, 1 + a:lower():byte() - string.byte("a"))
    end
    return table.concat(ns, " ")
end
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yas46 profile image
Yasser Beyer

JavaScript

let position = (str) => {
    const upper = str.trim().toUpperCase().split('');
    let arr = [];
    upper.map(l => (/^[a-z]+$/i.test(l)) && arr.push(l.charCodeAt(0)-64).toString())
    return arr.join(" ");
}

position("The sunset sets at twelve o' clock.");
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willsmart profile image
willsmart

A JS one-liner

alphaPosition = s => [...s.toLowerCase().replace(/[^a-z]/g, '')].map(c => c.charCodeAt(0) + 1 - 'a'.charCodeAt(0)).join(' ');

Output:

> alphaPosition("The sunset sets at twelve o' clock.")
< "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11"
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jesseleite profile image
Jesse Leite

In PHP using Laravel's Collection pipeline...

function alphabetPositions($string)
{
    return collect(str_split($string))
        ->map(function ($letter) {
            return collect(range('a', 'z'))->flip()->get(strtolower($letter));
        })
        ->filter()
        ->map(function ($key) {
            return $key + 1;
        })
        ->implode(' ');
}

echo alphabetPositions("The sunset sets at twelve o' clock.");

Will be cleaner when PHP gets shorthand arrow functions, which I believe are coming in 7.4 😍 ...

function alphabetPositions($string)
{
    return collect(str_split($string))
        ->map(fn($letter) => collect(range('a', 'z'))->flip()->get(strtolower($letter)))
        ->filter()
        ->map(fn($key) => $key + 1)
        ->implode(' ');
}

echo alphabetPositions("The sunset sets at twelve o' clock.");
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5422m4n profile image
Sven Assmann

solved in rust made with tests first :)

pub fn alphabet_position(s: &str) -> String {
  s.to_lowercase()
    .chars()
    .filter(|x| x.is_alphabetic())
    .map(|x| -> u8 { x as u8 - 'a' as u8 + 1 })
    .map(|x| -> String { x.to_string() })
    .collect::<Vec<String>>()
    .join(" ")
}

#[cfg(test)]
mod test {
  use super::*;

  #[test]
  fn it_should_relace_the_a_with_1() {
    let replaced = alphabet_position("a");
    assert_eq!(replaced, "1");
  }

  #[test]
  fn it_should_relace_the_capital_a_with_1() {
    let replaced = alphabet_position("A");
    assert_eq!(replaced, "1");
  }

  #[test]
  fn it_should_ignore_non_characters() {
    let replaced = alphabet_position("'a a. 2");
    assert_eq!(replaced, "1 1");
  }

  #[test]
  fn it_should_relace_the_sentence() {
    let replaced = alphabet_position("The sunset sets at twelve o' clock.");
    assert_eq!(
      replaced,
      "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11"
    );
  }
}
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choroba profile image
E. Choroba

Perl solution:

#!/usr/bin/perl
use warnings;
use strict;

sub alphabet_position {
    join ' ', map ord() - 96, grep /[a-z]/, split //, lc shift
}

use Test::More tests => 1;

is alphabet_position("The sunset sets at twelve o' clock."),
    '20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11';

Reading from the right: shift gets the argument, lc lower-cases it, split using an empty regex splits it into characters, grep removes all non-letters, ord returns the ASCII ordinal number of each letter, 97 corresponds to a; map replaces the characters by the numbers, join connects the numbers back to a string.

See join, map, ord, grep, split, lc, shift.

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citizen428 profile image
Michael Kohl

Perl6:

sub alphabet-position(Str $text) {
    $text.lc().split("").comb(/<:Ll>/).map({.ord() - 96}).join(" ")
}

Or alternatively with the feed operator (and no type annotation, TIMTOWTDI):

sub alphabet-position($text) {
    $text 
    ==> lc()
    ==> split("")
    ==> comb(/<:Ll>/)
    ==> map({.ord() - 96})
    ==> join(" ")
}

alphabet-position("The sunset sets at twelve o' clock.").say
# 20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11

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andre000 profile image
André Adriano

My take on this challenge, with Javascript

const encode = str => [...str.toLowerCase().replace(/[^a-z]/g, '')]
        .map(ch => ch.charCodeAt() - 96)
        .join(' ');

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jasman7799 profile image
Jarod Smith

so simple love it

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ryder_flynn profile image
Danish Flynn

"One-liner" (kind of) Ruby:

def alphabet_position(str)
  str.downcase.split('').select { |c| c =~ /[a-z]/ }.map { |c| c.ord - 96 }.join(' ')
end
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rione94 profile image
liễu nguyễn
def alphabet_position(str)
  str.downcase.gsub(/[^a-z]/, '').split('').map{|c| c.ord - 96}.join(' ')
end
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hanachin profile image
Seiei Miyagi

ruby <3

def alphabet_position(s)
  pos = (?a..?z |> zip 1..26 |> to_h)
  s |> downcase |> scan /[a-z]/ |> map &pos |> join ' '
end
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sonugan profile image
sonugan

C#

public static string AlphabetPosition(string text)
{
   return string.Join(" ", text
    .ToLower()
    .Where(c => char.IsLetter(c))
    .Select(c => (c - 'a') + 1)
    .ToList());
}
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b2aff6009 profile image
b2aff6009

A tiny python solutiuon:

def alphabet_position(text):
    converted = [str(ord(c) - ord('a') + 1) for c in text.lower() if c >= 'a']
    return " ".join(converted)
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alfredosalzillo profile image
Alfredo Salzillo

One line Javascript

const alphaPosition = str => [...str]
  .filter(letter => /[a-zA-Z]/.test(letter))
  .map(letter => letter.toLowerCase().charCodeAt(0) - 96)
  .join(' ')
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alexkhismatulin profile image
Alex Khismatulin
function alphabetPosition(text) {
  return text.toUpperCase().replace(/[^A-Z]/g, '').replace(/[A-Z]/g, str => str.charCodeAt() - 64 + ' ').trim();
}
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hectorpascual profile image
Héctor Pascual

Python :

lambda s : ' '.join([str(ord(c)-ord('a')+1) for c in s.lower() if re.search('[a-z]',c)])
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devparkk profile image