Solution to task 2

1 files changed, 70 insertions, 0 deletions

diff --git a/challenge-160/jo-37/perl/ch-2.pl b/challenge-160/jo-37/perl/ch-2.pl
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+++ b/challenge-160/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use List::Util 'sum0';
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [--] [I1 I2 ...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+I1 I2 ...
+    List of integers.
+
+EOS
+
+
+### Input and Output
+
+say equilibrium_index(@ARGV);
+
+
+### Implementation
+
+# The task does not specify if empty subarrays are allowed.  Assuming
+# they are allowed and have a sum of zero.
+sub equilibrium_index {
+    my ($i, $left, $right) = (0, 0, sum0 @_[1 .. $#_]);
+    # Starting with an empty left subarray, shift the index until an
+    # equilibrium is found or the right subarray becomes empty.
+    while ($left != $right && $i < $#_) {
+        $left += $_[$i++];
+        $right -= $_[$i];
+    }
+
+    $left == $right ? $i : -1;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is equilibrium_index(1, 3, 5, 7, 9), 3, 'example 1';
+        is equilibrium_index(1, 2, 3, 4, 5), -1, 'example 2';
+        is equilibrium_index(2, 4, 2), 1, 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is equilibrium_index(1, 1, 1, 3, -1), 2, 'negative element';
+        is equilibrium_index(1, -1, 2), 2, 'empty right subarray';
+        is equilibrium_index(2, 1, -1), 0, 'empty left subarray';
+        is equilibrium_index(1), 0, 'two empty subarrays';
+	}
+
+    done_testing;
+    exit;
+}