#+title: Challenge 188
#+date: 2022-10-27
#+html_link_up: ../
#+export_file_name: index
#+options: toc:nil
#+setupfile: ~/.emacs.d/org-templates/level-2.org

* Task 1 - Divisible Pairs

You are given list of integers @list of size $n and divisor $k.

Write a script to find out count of pairs in the given list that
satisfies the following rules.

The pair (i, j) is eligible if and only if
a) 0 <= i < j < len(list)
b) list[i] + list[j] is divisible by k


#+begin_src
Example 1
Input: @list = (4, 5, 1, 6), $k = 2
Output: 2

Example 2
Input: @list = (1, 2, 3, 4), $k = 2
Output: 2

Example 3
Input: @list = (1, 3, 4, 5), $k = 3
Output: 2

Example 4
Input: @list = (5, 1, 2, 3), $k = 4
Output: 2

Example 5
Input: @list = (7, 2, 4, 5), $k = 4
Output: 1
#+end_src

** Raku

Go over all combinations of elements as per rules and check if their sum
is divisible by divisor.

#+begin_src raku
unit sub MAIN(
    Int $divisor, *@list is copy where *.elems > 0
);
@list = @list>>.Int;

my Int $pairs;
for 0 ... @list.end -> $i {
    for $i ... @list.end -> $j {
        next if $i == $j;
        $pairs++ if (@list[$i] + @list[$j]) %% $divisor;
    }
}
put $pairs;
#+end_src