September 2017 Update

Task/Combinations/PHP/combinations-2.php

@@ -0,0 +1,48 @@
+<?php
+
+function combinations_set($set = [], $size = 0) {
+    if ($size == 0) {
+        return [[]];
+    }
+
+    if ($set == []) {
+        return [];
+    }
+
+
+    $prefix = [array_shift($set)];
+
+    $result = [];
+
+    foreach (combinations_set($set, $size-1) as $suffix) {
+        $result[] = array_merge($prefix, $suffix);
+    }
+
+    foreach (combinations_set($set, $size) as $next) {
+        $result[] = $next;
+    }
+
+    return $result;
+}
+
+function combination_integer($n, $m) {
+    return combinations_set(range(0, $n-1), $m);
+}
+
+assert(combination_integer(5, 3) == [
+    [0, 1, 2],
+    [0, 1, 3],
+    [0, 1, 4],
+    [0, 2, 3],
+    [0, 2, 4],
+    [0, 3, 4],
+    [1, 2, 3],
+    [1, 2, 4],
+    [1, 3, 4],
+    [2, 3, 4]
+]);
+
+echo "3 comb 5:\n";
+foreach (combination_integer(5, 3) as $combination) {
+    echo implode(", ", $combination), "\n";
+}