18图灵班作业15--二叉树遍历（前序）

思路

递归大法好！

代码

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> ans;
    void printTree(TreeNode* now){
        if(now==NULL) return;
        ans.push_back(now->val);
        printTree(now->left);
        printTree(now->right);
    }
    vector<int> preorderTraversal(TreeNode* root) {
        printTree(root);
        return ans;
    }
};