Go/goroutine: Project Euler 20-29

problem26.go

package main

import (
	"fmt"
	"runtime"
	"time"
)

func init() {
	runtime.GOMAXPROCS(8)
}

type nums []int

func (xs nums) member(n int) bool {
	for _, v := range xs {
		if n == v {
			return true
		}
	}
	return false
}

func cycle(n int, ch chan int) {
	xs := nums{}
	for x := 10 % n; !xs.member(x); x = 10 * x % n {
		xs = append(xs, x)
	}
	ch <- len(xs)
}

type queue struct {
	ch     chan int
	length int
}

func newQueue() queue {
	ch, ps := make(chan int, 1000), 0
	for n := 2; n < 1000; n++ {
		go cycle(n, ch)
		ps++
	}
	return queue{ch, ps}
}

func problem26() {
	max := 0
	for q := newQueue(); q.length > 0; q.length-- {
		if n := <-q.ch; n > max {
			max = n
		}
	}
	fmt.Println(max)
}

func main() {
	start := time.Now()
	problem26()
	fmt.Println(time.Now().Sub(start).Seconds())
}

problem27.go

package main

import (
	"fmt"
	"runtime"
	"time"
)

func init() {
	runtime.GOMAXPROCS(1000)
}

func isPrime(n int) bool {
	switch {
	case n < 2:
		return false
	case n == 2:
		return true
	case n%2 == 0:
		return false
	}
	for p := 3; p*p <= n; p += 2 {
		if n%p == 0 {
			return false
		}
	}
	return true
}

type pair struct {
	a, b, length int
}

func (x pair) mul() int {
	return x.a * x.b
}

func primeLength(a int, ch chan pair) {
	answer := pair{0, 0, 0}
	for b := 3; b < 1000; b += 2 {
		length := 0
		for n := 0; isPrime(n*n + a*n + b); n++ {
			length++
		}
		if length > answer.length {
			answer = pair{a, b, length}
		}
	}
	ch <- answer
}

type queue struct {
	ch     chan pair
	length int
}

func newQueue() queue {
	ch, ps := make(chan pair, 1000), 0
	for a := -999; a < 1000; a += 2 {
		go primeLength(a, ch)
		ps++
	}
	return queue{ch, ps}
}

func problem27() {
	answer := pair{0, 0, 0}
	for q := newQueue(); q.length > 0; q.length-- {
		if tmp := <-q.ch; tmp.length > answer.length {
			answer = tmp
		}
	}
	fmt.Println(answer.mul())
}

func main() {
	start := time.Now()
	problem27()
	fmt.Println(time.Now().Sub(start).Seconds())
}