515. Find Largest Value in Each Tree Row
Description Submission Solutions
- Total Accepted: 3804
- Total Submissions: 7252
- Difficulty: Medium
- Contributors: love_FDU_llp
You need to find the largest value in each row of a binary tree.
Example:
Input:
1
/
3 2
/
5 3 9
Output: [1, 3, 9]
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给定一颗二叉树，返回二叉树中每一层的最大值。
【思路】
这是一个典型的二叉树层序遍历的问题，需要使用队列来解决。关于java队列的使用，计划详细了解一下。
【java代码】
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */ 10 public class Solution { 11 public List<Integer> largestValues(TreeNode root) { 12 List<Integer> res = new ArrayList<>(); 13 Queue<TreeNode> queue = new LinkedList<>(); 14 15 if(root != null) queue.offer(root); 16 17 while(!queue.isEmpty()) { 18 int max = Integer.MIN_VALUE; 19 int size = queue.size(); 20 for(int i = 0; i < size; i++) { 21 TreeNode node = queue.poll(); 22 max = Math.max(max, node.val); 23 if(node.right != null) queue.offer(node.right); 24 if(node.left != null) queue.offer(node.left); 25 } 26 res.add(max); 27 } 28 29 return res; 30 } 31 }