Add solution 138.

Author: javadev

src/Algorithms/0138.copy-list-with-random-pointer/copy-list-with-random-pointer.php

@@ -0,0 +1,71 @@
+/*
+// Definition for a Node.
+class Node {
+    public $val;
+    public $next;
+    public $random;
+
+    @param Integer $val 
+    @param Node $next 
+    @param Node $random 
+    function __construct($val, $next, $random) {
+        $this->val = $val;
+        $this->next = $next;
+        $this->random = $random;
+    }
+}
+*/
+class Solution {
+
+    /**
+     * @param Node $head
+     * @return Node
+     */
+    function copyRandomList($head) {
+      $iter = $head;
+      $next;
+
+      // First round: make copy of each node,
+      // and link them together side-by-side in a single list.
+      while ($iter != null) {
+        $next = $iter->next;
+
+        $copy = new Node($iter->val, null, null);
+        $iter->next = $copy;
+        $copy->next = $next;
+
+        $iter = $next;
+      }
+
+      // Second round: assign random pointers for the copy nodes.
+      $iter = $head;
+      while ($iter != null) {
+        if ($iter->random != null) {
+          $iter->next->random = $iter->random->next;
+        }
+        $iter = $iter->next->next;
+      }
+
+      // Third round: restore the original list, and extract the copy list.
+      $iter = $head;
+      $pseudoHead = new Node(0, null, null);
+      $copy;
+      $copyIter = $pseudoHead;
+
+      while ($iter != null) {
+        $next = $iter->next->next;
+
+        // extract the copy
+        $copy = $iter->next;
+        $copyIter->next = $copy;
+        $copyIter = $copy;
+
+        // restore the original list
+        $iter->next = $next;
+
+        $iter = $next;
+      }
+
+      return $pseudoHead->next;
+    }
+}