## 1. Problem

199. 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

## 2. Solution

I solved this problem like this.

- We can solve this problem to bfs. Using deque!

```
class Solution:
def rightSideView(self, root: Optional[TreeNode]) -> List[int]:
ans = []
if root is None:
return ans
deq = deque([root])
while deq:
nodes = deq.copy()
deq.clear()
ans.append(nodes[-1].val)
for node in nodes:
if node.left is not None:
deq.append(node.left)
if node.right is not None:
deq.append(node.right)
return ans
```