Add solution 143.

Author: javadev

src/Algorithms/0143.reorder-list/reorder-list.php

@@ -0,0 +1,47 @@
+/**
+ * Definition for a singly-linked list.
+ * class ListNode {
+ *     public $val = 0;
+ *     public $next = null;
+ *     function __construct($val) { $this->val = $val; }
+ * }
+ */
+class Solution {
+
+    /**
+     * @param ListNode $head
+     * @return NULL
+     */
+    function reorderList($head) {
+        if($head == null) return;
+        $slow = $head;
+        $fast = $head;
+
+        while($fast != null && $fast->next != null){
+            $fast = $fast->next->next;
+            $slow = $slow->next;
+        }
+        
+        $next = null;
+        $curr = $slow;
+        $prev = null;
+        while($curr != null){
+            $next = $curr->next;
+            $curr->next = $prev;
+            $prev = $curr;
+            $curr = $next;
+        }
+        
+        $temp;
+        while($prev != null && $head->next != null){
+            $temp = $head->next;
+            $head->next = $prev;
+            $head = $temp;
+
+            $temp = $prev->next;
+            $prev->next = $head;
+            $prev = $temp;
+        }
+        $head->next = null;
+    }
+}