Leetcode-145. Binary Tree Postorder Traversal

题目

Given a binary tree, return the postorder traversal of its nodes’ values.

For example:
Given binary tree {1,#,2,3},
return [3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?
求二叉树的后序遍历结果，用循环不用递归

代码

class Solution {
public:
    vector<int> postorderTraversal(TreeNode *root) {
        vector<int> path;
        if(root==NULL)return path;

        stack<TreeNode*> stk;
        stk.push(root);
        TreeNode* cur = NULL;
        while(!stk.empty()) {
            cur = stk.top();
            if(cur->left ==NULL && cur->right ==NULL) {
                path.push_back(cur->val);
                stk.pop();
            } else {
                if(cur->right) {
                    stk.push(cur->right);
                    cur->right = NULL;
                }
                if(cur->left) {
                    stk.push(cur->left);
                    cur->left = NULL;
                }
            }
        }
        return path;
    }
};