A-M baby

Task/Knuths-algorithm-S/PHP/knuths-algorithm-s.php

@@ -0,0 +1,28 @@
+<?php
+function s_of_n_creator($n) {
+    $sample = array();
+    $i = 0;
+    return function($item) use (&$sample, &$i, $n) {
+        $i++;
+        if ($i <= $n) {
+            // Keep first n items
+            $sample[] = $item;
+        } else if (rand(0, $i-1) < $n) {
+            // Keep item
+            $sample[rand(0, $n-1)] = $item;
+        }
+        return $sample;
+    };
+}
+
+$items = range(0, 9);
+
+for ($trial = 0; $trial < 100000; $trial++) {
+    $s_of_n = s_of_n_creator(3);
+    foreach ($items as $item)
+        $sample = $s_of_n($item);
+    foreach ($sample as $s)
+        $bin[$s]++;
+}
+print_r($bin);
+?>