monte-carlo-pi.go

package main

import (
	"math/rand"
	"runtime"
	"fmt"
)

const TEST_COUNT = 100000000

// Calculates PI using Monte-Carlo method
func main() {
	numOfCpu := runtime.NumCPU()

	c := make(chan int, numOfCpu)

	for i := 0; i < numOfCpu; i++ {
		go func (n int) {
			inside := runner(n)
			fmt.Println(inside, "out of", n)
			c <- inside
		}(TEST_COUNT / numOfCpu)
	}

	result := make([]int, numOfCpu)
	for i := 0; i < numOfCpu; i++ {
		result[i] = <-c
	}

	insideCount := sum(result)
	fmt.Println(float64(insideCount) / TEST_COUNT * 4)
}

func sum(a []int) int {
	result := 0

	for _, n := range a {
		result += n
	}

	return result
}

func runner(n int) int {
	count := 0

	for i := 0; i < n; i++ {
		x := rand.Float64()
		y := rand.Float64()

		if (x * x + y * y < 1) {
			count++
		}
	}

	return count
}