Uncommon words

You are given two sentences. Write a script to return list of all uncommon words, order is not important.

Examples

Example 1
Input: $sentence1 = 'apple banana apple'
       $sentence2 = 'banana orange'
Output: ('orange')

Example 2
Input: $sentence1 = 'cat dog'
       $sentence2 = 'bird fish'
Output: ('cat', 'dog', 'bird', 'fish')

Example 3
Input: $sentence1 = 'the quick brown fox'
       $sentence2 = 'the quick'
Output: ('brown', 'fox')

Example 4
Input: $sentence1 = 'hello'
       $sentence2 = 'hello'
Output: ()

Example 5
Input: $sentence1 = 'blue blue red'
       $sentence2 = 'red green green yellow'
Output: ('yellow')

Analysis

From the examples I deduce 'uncommon' in this challenge means 'appears only once', and that is easily solved by counting the frequency of each word and reporting on those with frequency 1.

One could suggest that the sample size is rather small to deduce that a word is uncommon, and indeed in Example 4 above, 'hello' is classed as uncommon despite being 100% of the studied sample. But let's not quibble.

Try it 

#!/usr/bin/perl

# Blog: http://ccgi.campbellsmiths.force9.co.uk/challenge/385/1

use v5.26;    # The Weekly Challenge - 2026-08-03
use utf8;     # Week 385 - task 1 - Uncommon words
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';
use Encode;

uncommon_words('the cat sat on the mat', 'the dog sat on the rug');
uncommon_words('house', 'house');
uncommon_words('apple banana apple', 'banana orange');
uncommon_words('blue blue red', 'red green green yellow');

sub uncommon_words {
    
    my ($words, %freq, $uncommon);
    
    # initialise
    $words = lc(qq[$_[0] $_[1]]);
    $uncommon = '';
    
    # count frequencies
    $freq{$1} ++ while $words =~ m|([a-z]+)|g;
    
    # check for frequency 1
    $uncommon .= ($freq{$_} == 1 ? qq['$_', ] : '') for keys %freq;
    $uncommon = 'none  ' unless $uncommon;
    
    say qq[\nInput:  \$sentence1 = '$_[0]',];
    say qq[        \$sentence2 = '$_[1]'];
    say qq[Output: ] . substr($uncommon, 0, -2);
}

10 lines of code

Output from script

Input:  $sentence1 = 'the cat sat on the mat',
        $sentence2 = 'the dog sat on the rug'
Output: 'cat', 'mat', 'dog', 'rug'

Input:  $sentence1 = 'house',
        $sentence2 = 'house'
Output: none

Input:  $sentence1 = 'apple banana apple',
        $sentence2 = 'banana orange'
Output: 'orange'

Input:  $sentence1 = 'blue blue red',
        $sentence2 = 'red green green yellow'
Output: 'yellow'