二叉树非递归方式遍历

#include <bits/stdc++.h>

using namespace std;

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */


class TreeNode {
public:
    int val;
    TreeNode *left, *right;
    TreeNode(int val) {
        this->val = val;
        this->left = this->right = NULL;
    }
};

class Solution {
public:
    /**
     * @param root: The root of binary tree.
     * @return: Preorder in vector which contains node values.
     */
    struct record{
        TreeNode* tn;
        int state;
        record(TreeNode* tn, int state):tn(tn),state(state){}
    };
    vector<int> preorderTraversal(TreeNode *root) {
        // write your code here
        vector<int> ans;
        TreeNode* cur = root;
        stack<record> s;
        int state = 0;
        while(1){
            if(cur == NULL || (cur && state == 2)){
                if(cur == root) break;
                record tmp = s.top();
                cur = tmp.tn;
                state = tmp.state;
                s.pop();
            } else if(state == 0){
                ans.push_back(cur->val);
                s.push(record(cur, 1));
                cur = cur -> left;
            } else if(state == 1){
                s.push(record(cur, 2));
                cur = cur -> right;
                state = 0;
            }
        }
        return ans;
    }
};

int main(){

}