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                             CHALLENGE 188

                                Andinus
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                               2022-10-27





1 Task 1 - Divisible Pairs
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  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


  ┌────
  │ 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
  └────


1.1 Raku
────────

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

  ┌────
  │ 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;
  └────