Euler Problem 43

problem43.go

package main

import (
    "fmt"
    "time"
)

func to_integer(slice []int) int64 {
    k := int64(0)
    for i := 0; i < len(slice); i++ {
        k = int64(10)*k + int64(slice[i])
    }
    return k
}

func nextPermutation(slice []int) bool {
    var k int
    for k = len(slice) - 2; k >= 0; k-- {
        if slice[k] < slice[k+1] {
            break
        }
    }

    if k == -1 {
        return false
    }

    var l int
    for l = len(slice) - 1; l >= 0; l-- {
        if slice[k] < slice[l] {
            break
        }
    }

    slice[k], slice[l] = slice[l], slice[k]

    for i, j := k+1, len(slice)-1; i < j; i, j = i+1, j-1 {
        slice[i], slice[j] = slice[j], slice[i]
    }

    return true
}

func checkDivisibility(d []int) bool {
    if to_integer(d[1:4])%2 != 0 {
        return false
    }
    if to_integer(d[2:5])%3 != 0 {
        return false
    }
    if to_integer(d[3:6])%5 != 0 {
        return false
    }
    if to_integer(d[4:7])%7 != 0 {
        return false
    }
    if to_integer(d[5:8])%11 != 0 {
        return false
    }
    if to_integer(d[6:9])%13 != 0 {
        return false
    }
    if to_integer(d[7:10])%17 != 0 {
        return false
    }
    return true
}

func main() {
    d := []int{1, 0, 2, 3, 4, 5, 6, 7, 8, 9}

    t0 := time.Now()

    sum := int64(0)
    if checkDivisibility(d) {
        sum += to_integer(d)
    }
    for nextPermutation(d) {
        if checkDivisibility(d) {
            sum += to_integer(d)
        }
    }

    t1 := time.Now()

    fmt.Println(sum)
    fmt.Printf("Time taken: %v\n", t1.Sub(t0))
}