[数据结构与算法]LeetCode 589 N叉树前序遍历[DFS] HERODING的LeetCode之路

解题思路：
标准的前序遍历模板，只用把左右子树换成遍历整个数组就好，步骤都是一样的，代码如下：

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
private:
    vector<int> ans;
public:
    vector<int> preorder(Node* root) {
        dfs(root);
        return ans;
    }

    void dfs(Node* root) {
        if(root == nullptr) return;
        ans.push_back(root->val);
        int len = root->children.size();
        for(int i = 0; i < len; i ++) {
            dfs(root->children[i]);
        }
    }
};