1. 题目

2. 解题

2.1 递归

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

2.2 循环

• 利用先序，改一下，得到 根右左，最后反转 左右根（后序）

class Solution {
public:vector<int> postorder(Node* root) {if(root == NULL)return {};vector<int> ans;stack<Node*> stk;stk.push(root);Node *tp;int i, k;while(!stk.empty()){tp = stk.top();k = tp->children.size();ans.push_back(tp->val);stk.pop();i = 0;while(i<k)stk.push(tp->children[i++]);}//上面得到的是根右左，逆序return得到左右根(后序)return vector<int> (ans.rbegin(), ans.rend());}
};