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.

Try it 

#!/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