题解 | #二叉树的前序遍历#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
class Solution {
public:
    void ulr(TreeNode* root,vector<int>& ret)
    {
        if(root == nullptr) return ;
        ret.push_back(root->val);
        ulr(root->left,ret);
        ulr(root->right,ret);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        // write code here
        vector<int> ret;
        ulr(root,ret);
        return ret;
    }
};