package main

import (
	"fmt"
	"sync"
	"time"
)

func reduce(arr []float64) float64 {
	for count := len(arr); count > 1; {
		countNext := 1 + (count-1)/2
		wg := sync.WaitGroup{}
		for i := 0; i < countNext; i++ {
			wg.Add(1)
			go func(i int) {
				if i+countNext < count {
					arr[i] = arr[i] + arr[i+countNext]
				}
				wg.Done()
			}(i)
		}
		wg.Wait()
		count = countNext
	}
	return arr[0]
}

func iterate(arr []float64) float64 {
	var sum float64 = 0
	for i := 0; i < len(arr); i++ {
		sum += arr[i]
	}
	return sum
}

func main() {
	length := 1000000
	{
		arr := make([]float64, length)
		for i := 0; i < length; i++ {
			arr[i] = float64(i)
		}
		t := time.Now()
		fmt.Println("Sum: ", reduce(arr))
		fmt.Println(time.Now().Sub(t).Seconds())
	}
}