Challenge 051 task 1

1 files changed, 78 insertions, 0 deletions

diff --git a/challenge-051/jo-37/perl/ch-1.pl b/challenge-051/jo-37/perl/ch-1.pl
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+++ b/challenge-051/jo-37/perl/ch-1.pl
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+#!/usr/bin/perl -s
+
+use v5.24;
+use Test2::V0;
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV > 3;
+usage: $0 [-examples] [-tests] [TARGET N1 N2 N3...]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+TARGET
+    target sum for three summands
+
+N1 N2 N3
+    list of at least three numbers
+
+EOS
+
+
+### Input and Output
+
+main: {
+    local $" = ',';
+    local $, = ',';
+    say map "(@$_)", three_sum(@ARGV)->@*;
+}
+
+
+### Implementation
+
+# Taken from https://en.wikipedia.org/wiki/3SUM#Quadratic_algorithm:
+# Look up the required complement for each pair in a hash table.
+
+sub three_sum {
+    my $target = shift;
+    my @l = sort {$a <=> $b} @_;
+
+    my %l;
+    @l{@l} = ();
+    my @res;
+    for my $p (0 .. $#l - 2) {
+        my $a = $l[$p];
+        for my $q ($p + 1 .. $#l - 1) {
+            my $b = $l[$q];
+            my $c = $target - $a - $b;
+            push @res, [$a, $b, $c] if $c >= $b && exists $l{$c}
+        }
+    }
+    \@res;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is three_sum(0, -25, -10, -7, -3, 2, 4, 8, 10), 
+            bag {item [-10, 2, 8]; etc;}, 'example';
+
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+	}
+
+    done_testing;
+    exit;
+}