Equal strings

You are given three strings. You are allowed to remove the rightmost character of a string to make all equal. Write a script to return the number of operations to make it equal otherwise -1.

Examples

Example 1
Input: $s1 = "abc", $s2 = "abb", $s3 = "ab"
Output: 2
Operation 1: Delete "c" from the string "abc"
Operation 2: Delete "b" from the string "abb"

Example 2
Input: $s1 = "ayz", $s2 = "cyz", $s3 = "xyz"
Output: -1

Example 3
Input: $s1 = "yza", $s2 = "yzb", $s3 = "yzc"
Output: 3

Analysis

My approach to this is:

• Count the total number of characters ($all) in all three strings
• Count the number of characters ($n) that match in all 3 strings
• The answer is $all - 3 * $n

There is an edge case where all 3 strings are identical and we return 0.

Smart move for catching the edge case. Well documented solution and bonus DIY tool as always. Super cool, keep it up.

This review may cover either or both challenges for this week.

Try it 

Try running the script with any input:

Your @strings =

example: horse, house, hoarse

⤡

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge

use v5.26;    # The Weekly Challenge - 2025-03-24
use utf8;     # Week 314 - task 1 - Equal strings
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

equal_strings('abc', 'abb', 'ab');
equal_strings('ayz', 'cyz', 'xyz');
equal_strings('yza', 'yzb', 'yzc');

equal_strings('', 'ijk', 'ijk');
equal_strings('mno', '', '');
equal_strings('abc', 'abc', 'abc');
equal_strings('ab', 'abc', 'abc');
equal_strings('abcd', 'abc', 'abc');

sub equal_strings {
    
    my (@strings, $all, $keep, $n, $test);
    
    # initialise
    @strings = @_;
    say qq[\nInput:  \@strings = ('] . join(qq[', '], @strings) . qq[')];
    
    # get total characters in all strings
    $all += length($_) for @strings;
    
    # check match of first 1, 2 ... chars
    for $n (1 .. 99) {
        $test = substr($strings[0], 0, $n);
        
        # if they all match keep going
        if (substr($strings[1], 0, $n) eq $test and substr($strings[2], 0, $n) eq $test) {
            $keep += 3;
        
        # else we're done
        } else {
            say qq[Output: ] . ($keep ? $all - $keep : -1);
            return;
        }
    }
    
    # but there is an edge case where all 3 match
    say qq[Output: 0];
    return;
}

14 lines of code

Output from script

Input:  @strings = ('abc', 'abb', 'ab')
Output: 2

Input:  @strings = ('ayz', 'cyz', 'xyz')
Output: -1

Input:  @strings = ('yza', 'yzb', 'yzc')
Output: 3

Input:  @strings = ('', 'ijk', 'ijk')
Output: -1

Input:  @strings = ('mno', '', '')
Output: -1

Input:  @strings = ('abc', 'abc', 'abc')
Output: 0

Input:  @strings = ('ab', 'abc', 'abc')
Output: 2

Input:  @strings = ('abcd', 'abc', 'abc')
Output: 1