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+#!perl
+use strict;
+use warnings FATAL => qw(all);
+
+=prompt
+You are given an array of integers having four or more elements.
+
+Write a script to find two pairs of numbers from this list (four numbers total) so that the difference between their products is as large as possible.
+
+In the end return the max difference.
+
+    With Two pairs (a, b) and (c, d), the product difference is (a * b) - (c * d).
+
+
+Example 1
+
+Input: @ints = (5, 9, 3, 4, 6)
+Output: 42
+
+Pair 1: (9, 6)
+Pair 2: (3, 4)
+Product Diff: (9 * 6) - (3 * 4) => 54 - 12 => 42
+
+
+Example 2
+
+Input: @ints = (1, -2, 3, -4)
+Output: 10
+
+Pair 1: (1, -2)
+Pair 2: (3, -4)
+
+
+Example 3
+
+Input: @ints = (-3, -1, -2, -4)
+Output: 10
+
+Pair 1: (-1, -2)
+Pair 2: (-3, -4)
+
+
+Example 4
+
+Input: @ints = (10, 2, 0, 5, 1)
+Output: 50
+
+Pair 1: (10, 5)
+Pair 2: (0, 1)
+
+
+Example 5
+
+Input: @ints = (7, 8, 9, 10, 10)
+Output: 44
+
+Pair 1: (10, 10)
+Pair 2: (7, 8)
+
+=cut
+
+use List::Util qw(all); #  max product);
+
+use Test2::V0 -no_srand => 1;
+
+
+
+is(max_diff(5, 9, 3, 4, 6), 42, 'Example 1');
+is(max_diff(1, -2, 3, -4), 10, 'Example 2');
+is(max_diff(-3, -1, -2, -4), 10, 'Example 3');
+is(max_diff(10, 2, 0, 5, 1), 50, 'Example 4');
+is(max_diff(7, 8, 9, 10, 10), 44, 'Example 5');
+is(max_diff(-5, 1, 2, 3, 5), 31, 'Example 6a');
+is(max_diff(-5, -1, 2, 3, 5), 31, 'Example 7a');
+done_testing();
+
+
+sub max_diff
+{
+     my @arr = @_;
+     if ( (all {$_ >= 0} @arr) or (all { $_ < 0 } @arr) )
+     {
+          @arr = sort {$a <=> $b} @arr;
+          if ( all {$_ >= 0} @arr )
+          {
+               return product(@arr[$#arr-1, $#arr]) - 
+                      product(@arr[0, 1]);
+          }
+          else # i.e. < 0
+          {
+               return product(@arr[0, 1]) - 
+                      product(@arr[$#arr-1, $#arr]);
+          }
+     }
+     else
+     {
+          my $max = (~0+1)*-1;
+          for my $i ( @arr )
+          {
+               for my $j ( @arr )
+               {
+                    next if $i == $j;
+                    for my $k ( @arr )
+                    {
+                         next if ($k == $j or $k == $i);
+                         for my $m ( @arr )
+                         {
+                              next if ($m == $k or $m == $j or $m == $i);
+                              my $first = product($i, $j);
+                              my $second = product($k, $m);
+                              $max = ($first - $second) > $max ? 
+                                     ($first - $second) : $max;
+                         }
+                    }
+               }
+          }
+          return $max;
+     }
+     
+
+}
+
+sub product
+{
+     return $_[0] * $_[1];
+}