Merge remote-tracking branch 'upstream/master'

1 files changed, 75 insertions, 0 deletions

diff --git a/challenge-109/brtastic/php/ch-2.php b/challenge-109/brtastic/php/ch-2.php
new file mode 100644
index 0000000000..304967ffae
--- /dev/null
+++ b/challenge-109/brtastic/php/ch-2.php
@@ -0,0 +1,75 @@
+<?php
+
+const EL_COUNT = 7;
+
+function permute($what)
+{
+	if (count($what) == 1) {
+		return [$what];
+	}
+
+	$options = [];
+
+	foreach($what as $el) {
+		$seen = 0;
+		array_push($options, ...array_map(
+			fn ($arr) => [$el, ...$arr],
+			permute(
+				array_filter(
+					$what,
+					fn ($subel)
+						=> $subel != $el || $seen++
+				)
+			)
+		));
+	}
+
+	return $options;
+}
+
+function four_squares($input)
+{
+	$results = [];
+
+	if (count($input) != EL_COUNT) {
+		return $results;
+	}
+
+	foreach (permute($input) as $case) {
+		$real_case = [0, ...$case, 0];
+		$summed_groups = array_map(
+			fn ($el)
+				=> array_sum(
+					array_map(
+						fn ($subel)
+							=> $real_case[$subel],
+					range($el, $el + 2))
+				),
+			array_filter(
+				array_keys($real_case),
+				fn ($el)
+					=> $el % 2 == 0 && $el <= count($real_case) - 2
+			)
+		);
+
+		$matching_first = array_filter(
+			$summed_groups,
+			fn ($el)
+				=> $el == $summed_groups[0]
+		);
+
+		if (count($matching_first) == count($summed_groups)) {
+			$case_results = [];
+			for ($letter = 'a'; $letter != 'h'; ++$letter) {
+				$case_results[$letter] = array_shift($case);
+			}
+
+			$results[] = $case_results;
+		}
+	}
+
+	return $results;
+}
+
+var_dump(four_squares(range(1, 7)));
+