Count common

You are given two array of strings, @str1 and @str2. Write a script to return the count of common strings in both arrays.

Examples

Example 1
Input: @str1 = ('perl', 'weekly', 'challenge')
       @str2 = ('raku', 'weekly', 'challenge')
Output: 2

Example 2
Input: @str1 = ('perl', 'raku', 'python')
       @str2 = ('python', 'java')
Output: 1

Example 3
Input: @str1 = ('guest', 'contribution')
       @str2 = ('fun', 'weekly', 'challenge')
Output: 0

Analysis

Well, this looked easy until I wondered about repeated strings. For example:

@str1 = ('fred', 'fred', 'fred');
@str2 = ('fred', 'fred');

Do we report 1, because 'fred' is the only string that appears in both arrays, or 2 because there are only 2 pairs of 'fred', or 3 because each of the three 'fred' strings in @str1 matches a string in @str2.

I decided to go with 2. if you rephrase the challenge as follows, then my solution gives the answer: 'How many times can you delete a string from @str1 and delete the same string from @str2'.

Deleting something from the middle of an array is messy, so I started by creating $one, which is a concatenation of the strings in @str1 using a '~' character as separator, and as the first and last character. Then I count the number of times I can do $one =~ s|~$s~|~| while iterating $s along @str2.

That algorithm also works for edge cases such as either of both arrays being empty.

Great detailed XOR operation is very interesting, and definitely not to be missed. Thanks for the contributions.

Try it 

#!/usr/bin/perl

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

use v5.26;    # The Weekly Challenge - 2025-02-10
use utf8;     # Week 308 - task 1 - Count common
use warnings; # Peter Campbell Smith
binmode STDOUT, ':utf8';

count_common(['fred', 'jim', 'max', 'john'], ['john', 'bill', 'fred', 'alex']);
count_common(['fred', 'fred', 'fred'], ['joe', 'joe']);
count_common(['fred', 'fred', 'fred'], ['fred', 'fred', 'alice']);
count_common(['fred', 'fred', 'fred'], []);
count_common([], ['fred', 'fred', 'fred']);
count_common([], []);
count_common(['axe', 'bean', 'cabbage', 'dog', 'egg'], ['egg', 'axe', 'cabbage', 'bean', 'dog']);

sub count_common {
    
    my (@str1, @str2, $one, $count, $s);
    
    @str1 = @{$_[0]};
    @str2 = @{$_[1]};
    $count = 0;
    
    # join @str1 into a string separated by ~
    $one = '~' . join('~', @str1) . '~';
    
    # count times we can delete a member of @str2 from the string
    for $s (@str2) {
        $count ++ if $one =~ s|~$s~|~|;
    }
    
    say qq[\nInput:  \@str1 = ('] . join(q[', '], @str1) . qw[')];
    say qq[        \@str2 = ('] . join(q[', '], @str2) . qw[')];
    say qq[Output: $count];
}

11 lines of code

Output from script

Input:  @str1 = ('fred', 'jim', 'max', 'john')
        @str2 = ('john', 'bill', 'fred', 'alex')
Output: 2

Input:  @str1 = ('fred', 'fred', 'fred')
        @str2 = ('joe', 'joe')
Output: 0

Input:  @str1 = ('fred', 'fred', 'fred')
        @str2 = ('fred', 'fred', 'alice')
Output: 2

Input:  @str1 = ('fred', 'fred', 'fred')
        @str2 = ('')
Output: 0

Input:  @str1 = ('')
        @str2 = ('fred', 'fred', 'fred')
Output: 0

Input:  @str1 = ('')
        @str2 = ('')
Output: 0

Input:  @str1 = ('axe', 'bean', 'cabbage', 'dog', 'egg')
        @str2 = ('egg', 'axe', 'cabbage', 'bean', 'dog')
Output: 5