TL;DR

Here we are with TASK #1 from The Weekly Challenge #222. Enjoy!

The challenge

You are given a list of positive integers, @ints.

Write a script to find the total matching members after sorting the list increasing order.

Example 1

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

Original list: (1, 1, 4, 2, 1, 2)
Sorted list  : (1, 1, 1, 2, 3, 4)

Compare the two lists, we found 3 matching members (1, 1, 2).

Example 2

Input: @ints = (5, 1, 2, 3, 4)
Output: 0

Original list: (5, 1, 2, 3, 4)
Sorted list  : (1, 2, 3, 4, 5)

Compare the two lists, we found 0 matching members.

Example 3

Input: @ints = (1, 2, 3, 4, 5)
Output: 5

Original list: (1, 2, 3, 4, 5)
Sorted list  : (1, 2, 3, 4, 5)

Compare the two lists, we found 5 matching members.

The questions

Oh my, this must come from the past or our fine host wants to tickle us with some controversy.

I mean, what are matching members?!?

The examples seem to indicate that you take the original list, then take a sorted copy of the original list, then compare items in the same positions and count how many of them match.

What is a match, though? It might be…

• … that the two integer values are the same.
• … that the two elements in the list are the same. If the list contains the same value twice, you might consider these two values as different members, like they are two twins that happen to share the same face but still are different people.
• … something I can’t think of.

Well, we’re going to assume that a 3 is a 3, however many times it appears, OK?!?

The solution

Sort and compare by value, that’s how we do things here!

#!/usr/bin/env raku
use v6;
sub MAIN (*@list) { put matching-members(@list) }

sub matching-members (Positional(Int()) $list) {
   return ($list «==» $list.sort).sum;
   # OR: ($list «==» $list.sort).grep({$_}).elems;
}

There are two solutions above because I’m not sure that there is a guarantee that a True boolean value will always turn into a 1 when regarded as a number. Anyway, it works.

Perl is similar, without the hyperstuff but with a similar shape involved:

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';
use List::Util 'sum';

say matching_members(@ARGV);

sub matching_members (@list) {
   my @sorted = sort { $a <=> $b } @list;
   return sum map { $list[$_] == $sorted[$_] ? 1 : 0 } 0 .. $#list;
}

This is it, stay safe!