LeetCode 102. 二叉树的层次遍历(Binary Tree Level Order Traversal) 8

102. 二叉树的层次遍历
102. Binary Tree Level Order Traversal

题目描述
给定一个二叉树，返回其按层次遍历的节点值。（即逐层地，从左到右访问所有节点）。

每日一算法2019/5/11Day 8LeetCode102. Binary Tree Level Order Traversal

例如:
给定二叉树: [3,9,20,null,null,15,7],

返回其层次遍历结果:

[
  [3],
  [9,20],
  [15,7]
]

Java 实现

import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int x) {
        val = x;
    }
}

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> result = new LinkedList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if (root == null) {
            return result;
        }
        queue.offer(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> list = new LinkedList<>();
            for (int i = 0; i < size; i++) {
                if (queue.peek().left != null) {
                    queue.offer(queue.peek().left);
                }
                if (queue.peek().right != null) {
                    queue.offer(queue.peek().right);
                }
                list.add(queue.poll().val);
            }
            result.add(list);
        }
        return result;
    }
}

相似题目

参考资料