Task — First unique character

You are given a string, $s. Write a script to find out the first unique character in the given string and print its index (0-based).

Examples

Example 1
Input: $s = "Perl Weekly Challenge"
Output: 0 as 'P' is the first unique character

Example 2
Input: $s = "Long Live Perl"
Output: 1 as 'o' is the first unique character

Analysis

I had high hopes for:

$s =~ m|^(.*?)(.)([^\2]*)$|

which says:

• zero or more characters, followed by
• one character (the answer), followed by
• any number of characters that aren't the answer.

But it doesn't work, and I'm not sure why.

So I settled for cycling through the characters and searching for a further occurrence of each; when none is found, we have the answer.

Try it 

Try running the script with any input:

Your $s =

example: spam, spam, spam or spam

⤡

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2022-08-29
use utf8;     # Week 180 - task 1 - First unique character
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

first_unique_character('Perl Weekly Challenge');
first_unique_character('Long Live Perl');
first_unique_character('Cheer Cheer Cheer');

sub first_unique_character {
    
    my ($str, $j, $char);
    
    $str = shift;
    say qq[\nInput:  \$s = '$str'];
    
    # loop over characters
    for $j (0 .. length($str) - 1) {
        $char = substr($str, $j, 1);
        
        # no good if it recurs
        next if $str =~ m|^(.*)$char.*$char.*$|;
        
        # found the answer
        say qq[Output: $j (character = '$char')];
        return;
    }
    
    # no non-repeating character
    say qq[Output: -1];
}

Output

Input:  $s = 'Perl Weekly Challenge'
Output: 0 (character = 'P')

Input:  $s = 'Long Live Perl'
Output: 1 (character = 'o')

Input:  $s = 'Cheer Cheer Cheer'
Output: -1