Week 152 Task 2

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diff --git a/challenge-152/cheok-yin-fung/perl/ch-2.pl b/challenge-152/cheok-yin-fung/perl/ch-2.pl
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+#!/usr/bin/perl
+# The Weekly Challenge 152
+# Task 2 Rectangle Area
+# Usage: 
+# $ ch-2.pl [bottom-left of R1] [top-right of R1] [BL of R2] [TR of R2]
+#  e.g. 
+# $ ch-2.pl -1 0 2 2 0 -1 4 4  (Example 1)
+
+use strict;
+use v5.22.0;
+
+say rect_area(@ARGV[0..7]) 
+    if (defined($ARGV[0]) && defined($ARGV[7]) && verify(@ARGV[0..7]));
+
+
+
+sub verify {
+    my @A, my @B;
+    ($A[0], $A[1], $A[2], $A[3], $B[0], $B[1], $B[2], $B[3]) = @_;
+    my $pass_A = $A[0] < $A[2] && $A[1] < $A[3];
+    my $pass_B = $B[0] < $B[2] && $B[1] < $B[3];
+               
+    die "Problem(s) in input data of the first rectangle.\n" if !$pass_A;
+    die "Problem(s) in input data of the second rectangle.\n" if !$pass_B;
+    return $pass_A && $pass_B;
+}
+
+
+
+sub rect_area {
+    my @A, my @B;
+    # ($lA,   $bA,   $rA,   $tA,   $lB,   $bB,   $rB,   $rB)
+      ($A[0], $A[1], $A[2], $A[3], $B[0], $B[1], $B[2], $B[3]) = @_;
+
+    my @w = sort {$a<=>$b} ($A[0], $A[2], $B[0], $B[2]);
+    my @h = sort {$a<=>$b} ($A[1], $A[3], $B[1], $B[3]);
+
+    my $area = 0;
+
+    for my $i (0..2) { for my $j (0..2) {
+        my $inA =    ($w[$j] >= $A[0]) && ($A[2] >= $w[$j+1])
+                  && ($h[$i+1] <= $A[3]) && ($A[1] <= $h[$i]);
+
+        my $inB =    ($w[$j] >= $B[0]) && ($B[2] >= $w[$j+1])
+                  && ($h[$i+1] <= $B[3]) && ($B[1] <= $h[$i]);
+
+        if ($inA || $inB) {
+            $area += ($w[$i+1]-$w[$i])*($h[$j+1]-$h[$j]);
+        }
+    }}
+
+=pod
+    Except one rectangle is inside the other rectangle,
+    the two rectangles can be enscribed into a larger rectangle
+    I divided the larger rectangle into 9 small rectangular regions;
+    then check if each small regions is inside rect. A or rect. B.
+    If yes, add the area of the small region into $area.
+=cut
+
+    return $area;
+}
+
+
+
+use Test::More tests => 4;
+
+ok ( rect_area(-1,0,2,2,0,-1,4,4) == 22 ), "Example 1";
+ok ( rect_area(-3,-1,1,3,-1,-3,2,2) == 25), "Example 2";
+ok ( rect_area(0,0,1,1,-1,-1,4,4) == 25), "Square within Square";
+ok ( rect_area(-3,-3,0,0,0,0,4,4) == 25), "Seperated Squares";
+