add prob #538(2nd); iterative solution

Author: randomwalk10

538_Convert_BST_to_Greater_Tree_2nd.cpp

@@ -0,0 +1,48 @@
+#include <stack>
+using namespace std;
+
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution {
+public:
+    TreeNode* convertBST(TreeNode* root) {
+		if(NULL==root) return NULL;
+		stack<TreeNode*> s_parent;
+		stack<bool> s_visited;
+		int res = 0;
+
+		s_parent.push(root);
+		s_visited.push(false);
+		while(!s_parent.empty()){
+			TreeNode* tmp_node = s_parent.top(); s_parent.pop();
+			bool tmp_visited = s_visited.top(); s_visited.pop();
+
+			if(tmp_visited){
+				tmp_node->val += res;
+				res = tmp_node->val;
+			}
+			else{
+				//left
+				if(tmp_node->left){
+					s_parent.push(tmp_node->left);
+					s_visited.push(false);
+				}
+				//self
+				s_parent.push(tmp_node);
+				s_visited.push(true);
+				//right
+				if(tmp_node->right){
+					s_parent.push(tmp_node->right);
+					s_visited.push(false);
+				}
+			}
+		}
+
+		return root;
+    }
+};