Leetcode 144 Binary Tree Preorder Traversal 二叉树

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     void dfs(vector<int> &ans,TreeNode *root){//二叉树的先序遍历
13         if(!root){
14             return;
15         }
16         ans.push_back(root->val);
17         dfs(ans,root->left);
18         dfs(ans,root->right);
19     }
20     vector<int> preorderTraversal(TreeNode *root) {
21         vector<int> ans;
22         dfs(ans,root);
23         return ans;
24     }
25 };