# LeetCode 199. Binary Tree Right Side View

## Description

https://leetcode.com/problems/binary-tree-right-side-view/

Given the `root` of 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 1:

```Input: root = [1,2,3,null,5,null,4]
Output: [1,3,4]
```

Example 2:

```Input: root = [1,null,3]
Output: [1,3]
```

Example 3:

```Input: root = []
Output: []
```

Constraints:

• The number of nodes in the tree is in the range `[0, 100]`.
• `-100 <= Node.val <= 100`

## Explanation

Conduct level order traverse. The last nodes of each level are the right-side nodes.

## Python Solution

``````# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
def rightSideView(self, root: Optional[TreeNode]) -> List[int]:
results = []

if not root:
return results

queue = []
queue.append(root)

while queue:
size = len(queue)

level = []
for i in range(size):
node = queue.pop(0)

level.append(node.val)

if node.left:
queue.append(node.left)

if node.right:
queue.append(node.right)

results.append(level[-1])

return results``````
• Time Complexity: O(N).
• Space Complexity: O(N).