LeetCode 515. 在每个树行中找最大值(Find Largest Value in Each Tree Row)

515. 在每个树行中找最大值
515. Find Largest Value in Each Tree Row

题目描述
You need to find the largest value in each row of a binary tree.

您需要在二叉树的每一行中找到最大的值。

LeetCode515. Find Largest Value in Each Tree Row

Example:

Input:

          1
         / \
        3   2
       / \   \  
      5   3   9 

Output: [1, 3, 9]

Java 实现
TreeNode Class

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

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

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

class Solution {
    public List<Integer> largestValues(TreeNode root) {
        List<Integer> res = new LinkedList<>();
        helper(root, res, 0);
        return res;
    }

    public void helper(TreeNode root, List<Integer> res, int depth) {
        if (root == null) {
            return;
        }
        if (depth == res.size()) {
            res.add(root.val);
        } else {
            res.set(depth, Math.max(res.get(depth), root.val));
        }
        helper(root.left, res, depth + 1);
        helper(root.right, res, depth + 1);
    }
}

参考资料

• https://leetcode.com/problems/find-largest-value-in-each-tree-row/
• https://leetcode-cn.com/problems/find-largest-value-in-each-tree-row/
• https://leetcode.com/problems/find-largest-value-in-each-tree-row/discuss/98971/9ms-JAVA-DFS-solution