二叉树的前序遍历
给你二叉树的根节点 root ,返回它节点值的 前序 遍历。
示例 1:
输入: root = [1,null,2,3] 输出: [1,2,3]
示例 2:
输入: root = [] 输出: []
示例 3:
输入: root = [1] 输出: [1]
示例 4:
输入: root = [1,2] 输出: [1,2]
示例 5:
输入: root = [1,null,2] 输出: [1,2]
提示:
- 树中节点数目在范围 [0, 100] 内
- -100 <= Node.val <= 100
我的代码:
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode() : val(0), left(nullptr), right(nullptr) {} * TreeNode(int x) : val(x), left(nullptr), right(nullptr) {} * TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {} * }; */ class Solution { public: vector<int> preorderTraversal(TreeNode* root) { vector<int> res; preorder(root, res); return res; } void preorder(TreeNode* root, vector<int> &res) { if (root == NULL) return; res.push_back(root->val); preorder(root->left, res); preorder(root->right, res); } };