binary_tree_right_side_view.py

"""
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

"""

# 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]:
        ans = []
        if not root:
            return ans
        queue = deque()
        queue.append(root)

        while queue:
            ans.append(queue[-1].val)
            n = len(queue)
            for _ in range(n):
                node = queue.popleft()

                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
        
        return ans