Odd number

You are given an array of positive integers, such that all the numbers appear even number of times except one number. Write a script to find that integer.

Examples

Example 1
Input: @N = (2, 5, 4, 4, 5, 5, 2)
Output: 5 as it appears 3 times in the array whereas all 
other numbers - 2 and 4 - appear exactly twice.

Example 2
Input: @N = (1, 2, 3, 4, 3, 2, 1, 4, 4)
Output: 4

Analysis

My vanilla solution is to pass through the array counting the number of occurrences of each entry, and then pass through the array of counts until finding an odd number.

Try it 

#!/usr/bin/perl

use v5.26;
use strict;
use warnings;

# PWC 130 task 1 - Peter Campbell Smith - 2021-09-13 

odd_number(1, 2, 3, 4, 3, 2, 1, 4, 4, 3, 4);

sub odd_number {
    
    my (@N, $j, %count);

    # get $count{$j} == number of instances of $j
    for $j (@_) {
        $count{$j} ++;
    }

    # look for the first instance of $count{$j} being odd                                                                 
    for $j (keys %count) {
        if ($count{$j} & 1) {
            say qq[\nInput:  ] . join(', ', @_);
            say qq[Output: $j];
            last;
        }
    }
}

9 lines of code

Output

Input:  1, 2, 3, 4, 3, 2, 1, 4, 4, 3, 4
Output: 3