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 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) {
        vector<int> res;
        preorder(res,root);
        return res;
    }
};