429. N-ary Tree Level Order Traversal

429. N-ary Tree Level Order Traversal

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題目

Leetcode題目

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:

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

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解決

假設樹有n個節點。

• 時間複雜度：O(n)
• 空間複雜度：O(n)

/*
// Definition for a Node.
class Node {
public:
    int val = NULL;
    vector<Node*> children;

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) {
        vector<vector<int> > result;
        if (!root) return result;
        queue<Node*> tree;
        tree.push(root);
        while (!tree.empty()) {
            vector<int> node(tree.size());
            for (int i = 0; i < node.size(); i++) {
                Node* temp = tree.front();
                node[i] = temp->val;
                for (auto n : temp->children) {
                    tree.push(n);
                }
                tree.pop();
            }
            result.push_back(node);
        }
        return result;
    }
};