Maximum Average Subtree

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- Tag: #postorder

Given the root of a binary tree, find the maximum average value of any subtree of that tree.

(A subtree of a tree is any node of that tree plus all its descendants. The average value of a tree is the sum of its values, divided by the number of nodes.)

Example 1:

Input: [5,6,1] Output: 6.00000 Explanation: For the node with value = 5 we have an average of (5 + 6 + 1) / 3 = 4. For the node with value = 6 we have an average of 6 / 1 = 6. For the node with value = 1 we have an average of 1 / 1 = 1. So the answer is 6 which is the maximum.

Note:

- The number of nodes in the tree is between 1 and 5000.
- Each node will have a value between 0 and 100000.
- Answers will be accepted as correct if they are within 10^-5 of the correct answer.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

- Solution:

// https://code.dennyzhang.com/maximum-average-subtree // Basic Ideas: dfs + post-order // Complexity: Time O(n), Space O(1) /** * Definition for a binary tree node. * type TreeNode struct { * Val int * Left *TreeNode * Right *TreeNode * } */ func dfs(root *TreeNode, max *float64) (sum int, cnt int) { if root == nil { return 0, 0 } lsum, lcnt := dfs(root.Left, max) rsum, rcnt := dfs(root.Right, max) sum, cnt = lsum + rsum + root.Val, lcnt + rcnt + 1 val := float64(sum)/float64(cnt) if val > *max { *max = val } return } func maximumAverageSubtree(root *TreeNode) float64 { res := float64(0) dfs(root, &res) return res }