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

Tree

Example 1:

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

Example 2:

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

Example 3:

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

Example 4:

Input: root = []
Output: []

Constraints:

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

Approach

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
from collections import deque


class Solution:
    def rightSideView(self, root: Optional[TreeNode]) -> List[int]:
        res = []
        q = deque([root])

        while q:
            rightSide = None
            qLen = len(q)

            for i in range(qLen):
                node = q.popleft()
                if node:
                    rightSide = node
                    q.append(node.left)
                    q.append(node.right)

            if rightSide:
                res.append(rightSide.val)

        return res