codekata-golang/08_largest_product_in_a_series/main.go

package main

import (
	"fmt"
	"strconv"
	"time"
)

var src = "73167176531330624919225119674426574742355349194934" +
	"96983520312774506326239578318016984801869478851843" +
	"85861560789112949495459501737958331952853208805511" +
	"12540698747158523863050715693290963295227443043557" +
	"66896648950445244523161731856403098711121722383113" +
	"62229893423380308135336276614282806444486645238749" +
	"30358907296290491560440772390713810515859307960866" +
	"70172427121883998797908792274921901699720888093776" +
	"65727333001053367881220235421809751254540594752243" +
	"52584907711670556013604839586446706324415722155397" +
	"53697817977846174064955149290862569321978468622482" +
	"83972241375657056057490261407972968652414535100474" +
	"82166370484403199890008895243450658541227588666881" +
	"16427171479924442928230863465674813919123162824586" +
	"17866458359124566529476545682848912883142607690042" +
	"24219022671055626321111109370544217506941658960408" +
	"07198403850962455444362981230987879927244284909188" +
	"84580156166097919133875499200524063689912560717606" +
	"05886116467109405077541002256983155200055935729725" +
	"71636269561882670428252483600823257530420752963450"

func main() {
	var nextSrc []int
	for len(src) > 0 {
		i, err := strconv.Atoi(src[0:1])
		if err != nil {
			panic(err)
		}
		nextSrc = append(nextSrc, i)
		src = src[1:]
	}
	t := time.Now()
	var next []int
	var out int
	var outS []int
	for {
		next, nextSrc = FetchNextAdjacent(13, nextSrc)
		if len(next) == 0 {
			break
		}
		var product = next[0:1][0]
		next = next[1:]
		for _, v := range next {
			product = product * v
		}
		if product > out {
			out = product
			outS = next
		}
	}

	fmt.Println("time:", time.Since(t))
	fmt.Println("the largest product is", out, outS)
}

func FetchNextAdjacent(n int, src []int) ([]int, []int) {
	if n >= len(src) {
		return []int{}, src
	}
	ret := make([]int, n)
	copy(ret, src[1:n+1])
	return ret, src[n+1:]
}