[LeetCode] Problem 199 - Binary Tree Right Side View

Posted on | In ,

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example

Input: [1,2,3,null,5,null,4]

Output: [1, 3, 4]

Explanation:

1
2
3
4
5
   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

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
public List<Integer> rightSideView(TreeNode root) {
    List<Integer> result = new ArrayList<>();

    if (root == null)
        return result;

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

    while (!queue.isEmpty()) {
        int size = queue.size();
        result.add(queue.peekLast().val);

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

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

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

    return result;
}