1 //前序遍历
2 //递归写法
3 /**
4 * Definition for a binary tree node.
5 * struct TreeNode {
6 * int val;
7 * TreeNode *left;
8 * TreeNode *right;
9 * TreeNode(int x) : val(x), left(NULL), right(NULL) {}
10 * };
11 */
12 class Solution {
13 public:
14 void preorder(TreeNode *root,vector<int> &res){
15 if(root==NULL) return;
16 res.push_back(root->val);
17 preorder(root->left,res);
18 preorder(root->right,res);
19 }
20 vector<int> preorderTraversal(TreeNode* root) {
21 vector<int> res;
22 preorder(root,res);
23 return res;
24 }
25 };
1 /** 先序遍历，栈实现
2 * Definition for a binary tree node.
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 vector<int> preorderTraversal(TreeNode* root) {
13 vector<int> res;
14 if(root==NULL) return res;
15 stack<TreeNode*> st;
16 st.push(root);
17 while(!st.empty()){
18 auto node=st.top();
19 res.push_back(node->val);
20 st.pop();
21 if(node->right!=NULL) st.push(node->right);
22 if(node->left!=NULL) st.push(node->left);
23 }
24 return res;
25 }
26 };
