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