刷题——二叉树的前序遍历
二叉树的前序遍历_牛客题霸_牛客网
双指针法：
/*** struct TreeNode {* int val;* struct TreeNode *left;* struct TreeNode *right;* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}* };*/
class Solution {
public:/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可** * @param root TreeNode类 * @return int整型vector*/void preorder(vector<int>&res, TreeNode* root){if(root == NULL) return;res.push_back(root->val);preorder(res, root->left);preorder(res, root->right);}vector<int> preorderTraversal(TreeNode* root) {// write code herevector<int>res;preorder(res,root);return res;}
};栈
vector<int> preorderTraversal(TreeNode* root)
{vector<int>res;if(root == NULL) return res;stack<TreeNode*>s;s.push(root);while(!s.empty()){TreeNode* node =s.top();s.pop(); if(node != NULL)res.push_back(node->val);//将栈顶元素，添加到数组中elsecontinue;if(node->right)s.push(node->right);if(node->left)s.push(node->left);}return res;
}