力扣hot100 二叉树的层序遍历 队列 广度优先搜索

Problem: 102. 二叉树的层序遍历

思路

‍ 路飞

复杂度

时间复杂度:

添加时间复杂度, 示例： $O(n)$

空间复杂度:

添加空间复杂度, 示例： $O(n)$

Code

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
 	public List> levelOrder(TreeNode root)
	{
		List> ans = new ArrayList<>();
		LinkedList q = new LinkedList<>();

		if (root == null)
			return ans;
		q.add(root);
		while (!q.isEmpty())
		{
			int n = q.size();
			ArrayList list = new ArrayList<>(n);
			while (n-- > 0)
			{
				TreeNode node = q.poll();
				list.add(node.val);
				if (node.left != null)
					q.add(node.left);
				if (node.right != null)
					q.add(node.right);
			}
			ans.add(list);
		}
		return ans;
	}
}