例如:
给定二叉树: [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回其层次遍历结果:
[
[3],
[9,20],
[15,7]
]
提示:
节点总数 <= 1000
注意:本题与主站 102 题相同:https://leetcode-cn.com/problems/binary-tree-level-order-traversal/
来源:力扣(LeetCode)
链接:https://leetcode.cn/problems/cong-shang-dao-xia-da-yin-er-cha-shu-ii-lcof
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也还是广度优先搜索。
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ class Solution { public List<List<Integer>> levelOrder(TreeNode root) { if (root == null) { return new ArrayList<List<Integer>>(); } List<List<Integer>> res = new ArrayList<>(); Queue<TreeNode> queue = new LinkedList<>(); queue.add(root); search(queue, res); return res; } private void search(Queue<TreeNode> queue, List<List<Integer>> res) { if (queue.isEmpty()) { return; } Queue<TreeNode> queue1 = new LinkedList<>(); List<Integer> list = new ArrayList<>(); while (!queue.isEmpty()) { TreeNode tree = queue.poll(); list.add(tree.val); if (tree.left != null) { queue1.add(tree.left); } if (tree.right != null) { queue1.add(tree.right); } } res.add(list); search(queue1, res); } }