[C++知识库]589. N 叉树的前序遍历 590. N 叉树的后序遍历 N 叉树没有中序遍历【每日一题】

589. N 叉树的前序遍历

思路

? ? ? ? ? 和二叉树的前后序遍历基本是一样的

/*
// 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> ans;
    vector<int> preorder(Node* root) {
        if (root!=nullptr){
            help(root);
        }
        return ans;
    }
    void help(Node* root){
        ans.push_back(root->val);
        for (auto child : root->children){
            help(child);
        }
    }
};

590. N 叉树的后序遍历

/*
// 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> ans;
    vector<int> postorder(Node* root) {
        // if (root != nullptr){
        //     help(root);
        // }
        help(root);
        
        return ans;
        
    }
    void help(Node* root){
        if  (root == nullptr){
            return;
        }
        for (auto child : root->children){
            help(child);
        }
        ans.push_back(root->val);
    }
};