764. N-ary Tree Level Order Traversal

• Difficulty: Easy

• Topics: Tree, Breadth-first Search

• Similar Questions:

  • Binary Tree Level Order Traversal

  • N-ary Tree Preorder Traversal

  • N-ary Tree Postorder Traversal

Problem:

Given an n-ary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example, given a 3-ary tree:

We should return its level order traversal:

[
     [1],
     [3,2,4],
     [5,6]
]

Note:

1. The depth of the tree is at most 1000.
2. The total number of nodes is at most 5000.

Solutions:

/*
// 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<vector<int>> levelOrder(Node* root) {
        if (root == nullptr)    return {};
        queue<Node*> q;
        q.push(root);

        vector<vector<int>> ret;

        while (!q.empty()) {
            int size = q.size();
            vector<int> level;
            for (int i = 0; i < size; ++i) {
                Node* node = q.front(); q.pop();
                level.push_back(node->val);
                for (auto& child : node->children) {
                    q.push(child);
                }
            }
            ret.push_back(level);
        }

        return ret;
    }
};