Solution to task 2

1 files changed, 87 insertions, 0 deletions

diff --git a/challenge-138/jo-37/perl/ch-2.pl b/challenge-138/jo-37/perl/ch-2.pl
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+#!/usr/bin/perl -s
+
+use v5.16;
+use Test2::V0;
+use experimental 'signatures';
+
+our ($tests, $examples);
+
+run_tests() if $tests || $examples;	# does not return
+
+die <<EOS unless @ARGV;
+usage: $0 [-examples] [-tests] [N]
+
+-examples
+    run the examples from the challenge
+ 
+-tests
+    run some tests
+
+N
+    Check if the square root of N is the sum of two or more splits of N
+
+EOS
+
+
+### Input and Output
+
+say 0 + root_sum(shift);
+
+
+### Implementation
+
+sub root_sum ($n) {
+    # Split N into at least two parts and compare the squared sum of the
+    # parts with N.
+    # There is no need to disallow leading zeros in any part (except the
+    # first), as these may be split-off as separate parts resulting in
+    # the same sum and a larger number of parts, e.g.
+    # 201: 2 + 01 or 2 + 0 + 1.
+    # The only exception are single digit numbers that cannot be split
+    # into two parts and therefore must not have leading zeros.
+    our $sum;
+    $n =~ m{
+        ^
+        (?=\d+$)    # Numbers only.
+        (?!0+.$)    # Forbid leading zeros for 1-digit numbers.
+        (?{local $sum = 0})   # Initialize and localize the part sum.
+        (?:
+            (.+)    # capture one part
+            (?{local $sum = $sum + $^N})    # backtracking-safe part sum
+        ){2,}       # two or more parts
+        $
+
+        # Check part sum for complete matches:
+        (?(?{$sum ** 2 != $n}) (*FAIL))
+    }x;
+}
+
+
+### Examples and tests
+
+sub run_tests {
+    SKIP: {
+        skip "examples" unless $examples;
+
+        is root_sum(81),    T(), 'example 1';
+        is root_sum(9801),  T(), 'example 2';
+        is root_sum(36),    F(), 'example 3';
+    }
+
+    SKIP: {
+        skip "tests" unless $tests;
+
+        is root_sum(1296),  T(), 'without zeros';
+        is root_sum(18),    F(), 'not a square';
+        is root_sum(0),     F(), 'zero';
+        is root_sum('00'),  F(), 'double zero';
+        is root_sum(1),     F(), 'one';
+        is root_sum('01'),  F(), 'one with leading zero';
+        is root_sum('001'), F(), 'one with leading zeros';
+        is root_sum('081'), T(), 'leading zero';
+        is root_sum(-abc),  F(), 'non-numeric';
+	}
+
+    done_testing;
+    exit;
+}