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// @Title: 二叉树的层平均值 (Average of Levels in Binary Tree)
// @Author: 15816537946@163.com
// @Date: 2019-11-25 16:42:01
// @Runtime: 8 ms
// @Memory: 6 MB
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
/*
func averageOfLevels(root *TreeNode) []float64 {
}
*/
/*
func averageOfLevels(root *TreeNode) []float64 {
	res := make([]float64, 0, 128)
	nodes := make([]float64, 1, 1024)
	fmt.Println("res ->",res)
	fmt.Println("node ->",nodes)
	return nil
}
*/
/*
func averageOfLevels(root *TreeNode) []float64 {
	res := make([]float64, 0, 128)

	nodes := make([]*TreeNode, 1, 1024)
	nodes[0] = root

	// 通过两个for操作，实现队列的功能
	for len(nodes) > 0 {
		n := len(nodes)
		var sum int

		for i := 0; i < n; i++ {
			sum += nodes[i].Val
			if nodes[i].Left != nil {
				nodes = append(nodes, nodes[i].Left)
			}
			if nodes[i].Right != nil {
				nodes = append(nodes, nodes[i].Right)
			}
		}

		res = append(res, float64(sum)/float64(n))
		nodes = nodes[n:]

	}

	return res
}
*/

func averageOfLevels(root *TreeNode) []float64 {
	res := make([]float64, 0, 128)
	nodes := make([]*TreeNode, 1, 1024)
	nodes[0] = root

	for len(nodes) > 0 {
		var sum int
		n := len(nodes)
		for i := 0; i < n; i++ {
			sum += nodes[i].Val
			if nodes[i].Left != nil {
				nodes = append(nodes, nodes[i].Left)
			}
			if nodes[i].Right != nil {
				nodes = append(nodes, nodes[i].Right)
			}
		}

		res = append(res, float64(sum)/float64(n))
		nodes = nodes[n:]
	}

	return res
}