LeetCode - 429. N-ary Tree Level Order Traversal

429. N-ary Tree Level Order Traversal - medium

문제

Given an n-ary tree, return the level order traversal of its nodes’ values.

Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).

제한사항

• The height of the n-ary tree is less than or equal to 1000
• The total number of nodes is between [0, 10^4]

입출력 예

Input: root = [1,null,3,2,4,null,5,6]
Output: [[1],[3,2,4],[5,6]]

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [[1],[2,3,4,5],[6,7,8,9,10],[11,12,13],[14]]

풀이

• DFS, BFS

/*
// 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<vector<int>> levelOrder(Node* root) {
        if(!root)
            return {};
        
        vector<vector<int>> ans;
        // 트리의 depth를 key로 가지며 해당 deptp의 원소들을 가진 vector를 value로 가진 map
        map<int, vector<int>> m;
        queue<pair<Node*, int>> q;
        
        // BFS
        q.push({root, 1});
        while(!q.empty()){
            auto node = q.front();
            q.pop();
            
            // 현재 deptp에 원소의 값을 추가
            m[node.second].push_back(node.first->val);
            
            for(const auto& i : node.first->children){
                q.push({i, node.second + 1});
            }
        }
        
        for(const auto& i : m)
            ans.push_back(i.second);
        
        return ans;
    }
};