Leetcode 144. Binary Tree Preorder Traversal二叉树前序遍历

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

Example:

Input: [1,null,2,3]1\2/3Output: [1,2,3]

题目链接:https://leetcode.com/problems/binary-tree-preorder-traversal/

/*** 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:void pre_order(TreeNode* root,vector<int>&res){if(root){res.emplace_back(root->val);pre_order(root->left,res);pre_order(root->right,res);}}vector<int> preorderTraversal(TreeNode* root) {vector<int> res;pre_order(root,res);return res;}
};

---------------------2019.8.12复习

-------------------2021年3月10日14:41:09

 

-----------------------2021年4月30日19:48:03

非递归方式

class Solution {
public:vector<int> preorderTraversal(TreeNode* root) {vector<int> res;if(!root){return res;}stack<TreeNode*> stk;stk.push(root);while(!stk.empty()){TreeNode *node=stk.top();stk.pop();res.push_back(node->val);if(node->right){stk.push(node->right);}if(node->left){stk.push(node->left);}}return res;}
};

 

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