[LeetCode] Problem 515 - Find Largest Value in Each Tree Row

Posted on | In ,

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

Example

Input: 

1
2
3
4
5
    1
   / \
  3   2
 / \   \  
5   3   9

Output: [1, 3, 9]

Code

1
2
3
4
5
6
public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
public List<Integer> largestValues(TreeNode root) {
    List<Integer> result = new ArrayList<>();

    if (root == null)
        return result;

    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);

    while (!queue.isEmpty()) {
        int size = queue.size();
        int max = Integer.MIN_VALUE;

        for (int i = 0; i < size; i++) {
            TreeNode node = queue.poll();
            max = Math.max(max, node.val);

            if (node.left != null)
                queue.offer(node.left);
            if (node.right != null)
                queue.offer(node.right);
        }

        result.add(max);
    }

    return result;
}