Add solution 99.

Author: javadev

src/Algorithms/0099.recover-binary-search-tree/recover-binary-search-tree.php

@@ -0,0 +1,34 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     public $val = null;
+ *     public $left = null;
+ *     public $right = null;
+ *     function __construct($value) { $this->val = $value; }
+ * }
+ */
+class Solution {
+
+    /**
+     * @param TreeNode $root
+     * @return NULL
+     */
+    function recoverTree($root) {
+        $stack = [];
+        $current = $root; $prev = null; $first = null; $second = null;
+        while ($current != null || count($stack) != 0) {
+            while ($current != null) {
+                array_push($stack, $current);
+                $current = $current->left;
+            }
+            $current = array_pop($stack);
+            if ($prev != null && $current->val < $prev->val) {
+                if ($first == null) $first = $prev;
+                $second = $current;
+            } 
+            $prev = $current; $current = $current->right;
+        }
+        // swap
+        $temp = $first->val; $first->val = $second->val; $second->val = $temp;        
+    }
+}