LeetCode 637. Average of Levels in Binary Tree

Description

https://leetcode.com/problems/average-of-levels-in-binary-tree/

Given the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted.

Example 1:

Input: root = [3,9,20,null,15,7]
Output: [3.00000,14.50000,11.00000]
Explanation: The average value of nodes on level 0 is 3, on level 1 is 14.5, and on level 2 is 11.
Hence return [3, 14.5, 11].

Example 2:

Input: root = [3,9,20,15,7]
Output: [3.00000,14.50000,11.00000]

Constraints:

  • The number of nodes in the tree is in the range [1, 104].
  • -231 <= Node.val <= 231 - 1

Explanation

Do breadth-first search and calculate average on levels.

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 averageOfLevels(self, root: TreeNode) -> List[float]:
        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(sum(level) / len(level))
        
        
        return results
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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