leetcode7:binary-tree-preorder-traversal

题目描述

求给定的二叉树的前序遍历。

例如：

给定的二叉树为{1,#,2,3},

1

  \

   2

  /

3

返回：[1,2,3].

备注；用递归来解这道题太没有新意了，可以给出迭代的解法么？

/**
 * struct TreeNode {
 *    int val;
 *    struct TreeNode *left;
 *    struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     *
     * @param root TreeNode类
     * @return int整型vector
     */
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        vector <int> res;
        stack<TreeNode*> s;
        if (root==NULL){
            return res;
        }
        s.push(root);
        while (!s.empty())
        {
            TreeNode *cur=s.top();
            s.pop();
            res.push_back(cur->val);
            if (cur->right!=NULL)
                s.push(cur->right);
            if (cur->left !=NULL)
                s.push(cur->left);
            
        }
        return res;
    }
};