tasks a-s

Task/Catalan-numbers/PHP/catalan-numbers.php

@@ -0,0 +1,33 @@
+<?php
+
+class CatalanNumbersSerie
+{
+  private static $cache = array(0 => 1);
+
+  private function fill_cache($i)
+  {
+    $accum = 0;
+    $n = $i-1;
+    for($k = 0; $k <= $n; $k++)
+    {
+      $accum += $this->item($k)*$this->item($n-$k);
+    }
+    self::$cache[$i] = $accum;
+  }
+  function item($i)
+  {
+    if (!isset(self::$cache[$i]))
+    {
+      $this->fill_cache($i);
+    }
+    return self::$cache[$i];
+  }
+}
+
+$cn = new CatalanNumbersSerie();
+for($i = 0; $i <= 15;$i++)
+{
+  $r = $cn->item($i);
+  echo "$i = $r\r\n";
+}
+?>