先序遍历递归和非递归解法 

 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 };

 

posted @ 2019-04-30 14:57  unique_ptr  阅读(301)  评论(0)    收藏  举报