solution.go

package main

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

const NUMBER = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450"

func ThirtheenAdjacentDigitsWithTheGreatestProduct() (maxProduct int) {
  firstIndex := -1
  lastIndex := 12

  for lastIndex < len(NUMBER) {
    firstIndex++; lastIndex++
    newProduct := 1

    for _, strValue := range NUMBER[firstIndex:lastIndex] {
      if strValue == '0' {
        break;
      }
      value, _ := strconv.Atoi(string(strValue))
      newProduct = newProduct * value
    }

    if newProduct > maxProduct {
      maxProduct = newProduct
    }
  }
  return
}

func main() {
  start := time.Now()
  result := ThirtheenAdjacentDigitsWithTheGreatestProduct()
  elapsed := time.Since(start)
  fmt.Printf("=> Result: %d\n", result)
  fmt.Printf("=> Time: %.8fs\n", elapsed.Seconds())
}