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).

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