429.N-ary Tree Level Order Traversal

Tags: Medium Tree Breadth-first Search

Links: https://leetcode.com/problems/n-ary-tree-level-order-traversal/

---

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).

Example 1:

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

Example 2:

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]]

Constraints:

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

---

/*
// 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) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        vector<vector<int>> res;
        if (!root) return res;

        queue<Node *> q;
        q.push(root);
        while (!q.empty()) {
            int n = q.size();
            vector<int> tmp;
            for (int i = 0; i < n; ++i) {
                Node *p = q.front(); q.pop();
                tmp.push_back(p -> val);
                auto & v = p -> children;
                for (auto e : v) q.push(e);
            }
            res.push_back(tmp);
        }

        return res;
    }
};