euler40.go

// Go solution to https://projecteuler.net/problem=40
package main                                                                                                                                                                                                
 
import (
    "fmt"
    "log"
    "strconv"
)  
   
func main() {
    n := 1
    b := make([]byte, 0, 1000000)
    for len(b) < 1000000 {
        b = append(b, []byte(fmt.Sprint(n))...)
        n++ 
    }   
   
    fmt.Println(n)
   
    product := 1
    for i := 0; i <= 1000000; i = ((i + 1) * 10) - 1 { 
        n, err := strconv.Atoi(string(b[i]))
        if err != nil {
            log.Fatal(err)
        }
        product *= n
    }   
   
    fmt.Println(product)
}

euler40.swift

import Foundation

var str = ""
var len = str.characters.count
var n = 1

while len < 1000000 {
	let nStr = String(n)
	len += nStr.characters.count
	str += nStr
	n++
}

print(n)

struct Product {
	let result: Int
	let index: Int

	func addDigit(digit: String) -> Product {
		guard let d = Int(digit) else {
			return self
		}

		return Product(result: result * d, index: ((index + 1) * 10) - 1)
	}
}

let product = str.characters
	.enumerate()
	.reduce(Product(result: 1, index: 0)) { (product, char) in
		if (char.index + 1) % (product.index + 1) == 0 {
			return product.addDigit(String(char.element))
		}

		return product
}

print(product.result)