MediumNo. 2265
Count Nodes Equal to Average of Subtree — LeetCode 2265 Python Solution
- Pattern
- Tree Traversal
- Topics
- Tree, Depth-First Search, Binary Tree
- Reading time
- 3 min
- Source
- leetcode.com
The problem
Given the root of a binary tree, return the number of nodes where the value of the node is equal to the average of the values in its subtree. Note: The average of n elements is the sum of the n elements divided by n and rounded down to the nearest integer.
Example
- Input
- root = [4,8,5,0,1,null,6]
- Output
- 5
- Explanation
- For the node with value 4: The average of its subtree is (4 + 8 + 5 + 0 + 1 + 6) / 6 = 24 / 6 = 4.
Python solution
class Solution:
def averageOfSubtree(self, root: TreeNode) -> int:
def dfs(root) -> tuple:
if not root:
return 0, 0
ls, ln = dfs(root.left)
rs, rn = dfs(root.right)
s = ls + rs + root.val
n = ln + rn + 1
nonlocal ans
ans += int(s // n == root.val)
return s, n
ans = 0
dfs(root)
return ansComplexity
- Time
- O(n)
- Space · auxiliary
- O(n)
Pattern: Tree Traversal
Choose the order — preorder, inorder, postorder, level — and the problem solves itself. LeetCode 2265. Count Nodes Equal to Average of Subtree is filed here because LeetCode tags it Tree and Binary Tree, which is the vocabulary this hub collects.
The tree traversal guide has the Python template for the pattern and the 225 LeetCode problems that use it.
Related problems
| No. | Problem | Difficulty |
|---|---|---|
| 0098 | Validate Binary Search Tree | Medium |
| 0099 | Recover Binary Search Tree | Medium |
| 0100 | Same Tree | Easy |
| 0101 | Symmetric Tree | Easy |
| 0104 | Maximum Depth of Binary Tree | Easy |
| 0110 | Balanced Binary Tree | Easy |
Frequently asked questions
- How hard is LeetCode 2265. Count Nodes Equal to Average of Subtree?
LeetCode 2265. Count Nodes Equal to Average of Subtree is rated Medium on LeetCode.
- What is the time complexity of LeetCode 2265. Count Nodes Equal to Average of Subtree?
The Python solution on this page runs in O(n).
- What is the space complexity of LeetCode 2265. Count Nodes Equal to Average of Subtree?
The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 2265. Count Nodes Equal to Average of Subtree cover?
LeetCode 2265. Count Nodes Equal to Average of Subtree is tagged Tree, Depth-First Search and Binary Tree on LeetCode.