590.N Ary Tree Postorder Traversal

590.N Ary Tree Postorder Traversal

难度:Easy

给定一个 N 叉树，返回其节点值的后序遍历。

例如，给定一个 3叉树 :

返回其后序遍历: [5,6,3,2,4,1].

说明: 递归法很简单，你可以使用迭代法完成此题吗?

• 递归法：

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

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<int> postorder(Node* root) {
        vector<int>res;
        if(!root) return res;
        for(auto i:root->children)
        {
            vector<int>tmp =postorder(i);
            res.insert(res.end(),tmp.begin(),tmp.end());
            }
        res.push_back(root->val);
        return res;
    }
};

• 迭代法：

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

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<int> postorder(Node* root) {
        vector<int>res;
        if(!root) return res;
        stack<Node*>pt;
        pt.push(root);
        while(!pt.empty())
        {
            if(pt.top()->children.empty())
            {
                res.push_back(pt.top()->val);
                pt.pop();
                if(!pt.empty()) pt.top()->children.erase(pt.top()->children.begin());
            }
            else{
                pt.push(pt.top()->children[0]);
            }
        }
        return res;
    }
};