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85 lines
1.5 KiB
Markdown
85 lines
1.5 KiB
Markdown
# [637. Average of Levels in Binary Tree](https://leetcode.com/problems/average-of-levels-in-binary-tree/)
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## 题目
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Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.
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**Example 1**:
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```
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Input:
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3
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/ \
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9 20
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/ \
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15 7
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Output: [3, 14.5, 11]
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Explanation:
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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].
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```
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**Note**:
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The range of node's value is in the range of 32-bit signed integer.
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## 题目大意
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按层序从上到下遍历一颗树，计算每一层的平均值。
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## 解题思路
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- 用一个队列即可实现。
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- 第 102 题和第 107 题都是按层序遍历的。
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## 代码
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```go
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package leetcode
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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func averageOfLevels(root *TreeNode) []float64 {
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if root == nil {
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return []float64{0}
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}
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queue := []*TreeNode{}
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queue = append(queue, root)
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curNum, nextLevelNum, res, count, sum := 1, 0, []float64{}, 1, 0
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for len(queue) != 0 {
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if curNum > 0 {
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node := queue[0]
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if node.Left != nil {
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queue = append(queue, node.Left)
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nextLevelNum++
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}
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if node.Right != nil {
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queue = append(queue, node.Right)
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nextLevelNum++
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}
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curNum--
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sum += node.Val
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queue = queue[1:]
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}
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if curNum == 0 {
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res = append(res, float64(sum)/float64(count))
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curNum, count, nextLevelNum, sum = nextLevelNum, nextLevelNum, 0, 0
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}
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}
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return res
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}
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``` |