Twice appearance

You are given a string, $str, containing lowercase English letters only. Write a script to print the first letter that appears twice.

Examples

Example 1
Input: $str = "acbddbca"
Output: "d"

Example 2
Input: $str = "abccd"
Output: "c"

Example 3
Input: $str = "abcdabbb"
Output: "a"

Analysis

I feel sure there's a neat way to do this with an exciting regular expression, but my solution is to iterate along the letters in the string, $a, and check whether:

$str =~ m|$a.*$a|;

... and if it does, we have the answer.

Interesting use of regex and we have pretty cool solutions in Perl. Thanks for sharing knowledge with us.

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

Try it 

Try running the script with any input:

Your $str =

example: challenge

⤡

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2024-07-29
use utf8;     # Week 280 - task 1 - Twice appearance
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

twice_appearance('acbddbca');
twice_appearance('abccd');
twice_appearance('abcdabbb');
twice_appearance('aabcdef');
twice_appearance('abcdeff');
twice_appearance('soporific');

sub twice_appearance {
    
    my ($str, $j, $a);
    $str = shift;
    
    # iterate along string
    for $j (0 .. length($str) - 1) {
        $a = substr($str, $j, 1);
        
        # check if this letter appears twice
        last if $str =~ m|$a.*$a|;
        $a = '';
    }
    printf(qq[\nInput:  \@str = '%s'\n], $str);
    printf(qq[Output: '%s'\n], $a);
}

9 lines of code

Output from script

Input:  @str  = 'acbddbca'
Output: 'a'

Input:  @str = 'abccd'
Output: 'c'

Input:  @str = 'abcdabbb'
Output: 'a'

Input:  @str = 'aabcdef'
Output: 'a'

Input:  @str = 'abcdeff'
Output: 'f'

Input:  @str = 'soporific'
Output: 'o'