1. 题目

2. 解题

2.1 递归

class Solution {
public:vector<int> preorder(Node* root) {vector<int> ans;preRec(root,ans);return ans;}void preRec(Node* root, vector<int> &ans) {if(root == NULL)return;ans.push_back(root->val);for(int i = 0; i < root->children.size(); ++i)preRec(root->children[i], ans);}
};

2.2 循环

class Solution {
public:vector<int> preorder(Node* root) {if(root == NULL)return {};vector<int> ans;stack<Node*> stk;Node *tp;int i;stk.push(root);while(!stk.empty()){tp = stk.top();ans.push_back(tp->val);i = tp->children.size();stk.pop();while(i){stk.push(tp->children[--i]);}}return ans;}
};