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199. Binary Tree Right Side View

Difficulty Topics

Description

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

Solution

binary-tree-right-side-view.py
# 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]:
        if not root: return []

        res = []

        queue = deque([root])

        while queue:
            n = len(queue)
            count = 0

            for i in range(n):
                node = queue.popleft()

                for child in (node.left, node.right):
                    if child:
                        queue.append(child)

                if i == n - 1:
                    res.append(node.val)

        return res