leetcode:Binary Tree Postorder Traversal

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<int> postorderTraversal(TreeNode *root) {        stack<int> statusStack;        stack<TreeNode *> traversalStack;        vector<int> result;        if(root == NULL)            return result;        statusStack.push(0);        traversalStack.push(root);        while(false == traversalStack.empty())        {            TreeNode * currentNode = traversalStack.top();            traversalStack.pop();            int currentStatus = statusStack.top();            statusStack.pop();            if(currentStatus == 1)            {                result.push_back(currentNode->val);            }            else            {                statusStack.push(1);                traversalStack.push(currentNode);                if(currentNode->right != NULL)                {                    statusStack.push(0);                    traversalStack.push(currentNode->right);                }                if(currentNode->left != NULL)                {                    statusStack.push(0);                    traversalStack.push(currentNode->left);                }            }        }        return result;    }};