/** * struct TreeNode { * int val; * struct TreeNode *left; * struct TreeNode *right; * }; */ #include <cstddef> #include <vector> class Solution { public: /** * * @param root TreeNode类 * @return int整型vector */ vector<int> preorderTraversal(TreeNode* root) { // write code here vector<int> res; preorder(root, res); return res; } void preorder (TreeNode* root, vector<int>& res) { if (!root) { return; } res.push_back(root->val); preorder(root->left, res); preorder(root->right, res); } };