[数据结构与算法]力扣-589题 N叉树的前序遍历（C++）- N叉树迭代前序遍历

题目链接：https://leetcode-cn.com/problems/n-ary-tree-preorder-traversal/
题目如下：

/*
// 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 {
public:
    vector<int> preorder(Node* root) {
        vector<int> result;
        if(root==NULL) return result;

        stack<Node*> stk;
        stk.push(root);

        while(!stk.empty()){
            Node* node=stk.top();
            stk.pop();

            if(node!=NULL) result.push_back(node->val);

            for(int i=node->children.size()-1;i>=0;i--){
                Node* temp=node->children[i];
                if(temp!=NULL) stk.push(temp);
            }
        }

        return result;       
    }
};