Daily Challenge #47 - Alphabets

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.

---

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

Comments

[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.

[Jarod Smith]

love how readable this is

[Amin]

Thank you sir!

[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.

[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).

[Héctor Pascual]

that's crazy

[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.

[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

[Aadi Bajpai]

Python one liner to the rescue 🙂

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

[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")
    );                                                                                         
}                                                                                              

[Jarod Smith]

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

[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.

[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) . (==)

[Sven Kanoldt]

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"
    );
  }
}

[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.