leetcode-144. Binary Tree Preorder Traversal c++

1、来源：144. Binary Tree Preorder Traversal

2、题目：

Given a binary tree, return the preorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

   1    \     2    /   3

return [1,2,3].

Note: Recursive solution is trivial, could you do it iteratively?

3、我的代码：

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    vector<int> preorderTraversal(TreeNode* root) {        stack<TreeNode*> s;        vector<int> v;        if(root==NULL)            return v;        s.push(root);        while(!s.empty()){            TreeNode*p=s.top();            v.push_back(p->val);            s.pop();            if(p->right!=NULL){                s.push(p->right);            }            if(p->left!=NULL){                s.push(p->left);            }        }        return v;    }};

4、参考：

    1）前序遍历

     2）vector的用法