LeetCode.429. N 叉树的层序遍历

LeetCode.429. N 叉树的层序遍历

难度：medium

 BFS：

N叉树的层序遍历相对于二叉树层序遍历的改动就是：在遍历一个节点的儿子们的时候需要用for去访问children的各个元素：

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
    public List<List<Integer>> levelOrder(Node root) {
        List<List<Integer>> ansList = new ArrayList<>();
        Queue<Node> queue = new LinkedList<>();
        if (root == null) {
            return ansList;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            List<Integer> levelList = new ArrayList<>();
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                Node node = queue.poll();
                levelList.add(node.val);
                // (1)
                int levelSize = node.children.size();
                for (int j = 0; j < levelSize; j++) {
                    queue.offer(node.children.get(j));
                }
                // (2)
                //queue.addAll(node.children);
            }
            ansList.add(levelList);
        }

        return ansList;
    }
}