kred...

gistfile1.java

card = "446157xxxxxx3246"

firstx = card.indexOf('x')
lastx = card.lastIndexOf('x')

firstnum = card[0..firstx-1]
lastnum = card[lastx+1..-1]

xlen = lastx-firstx+1

def luhn(cardNum){
    total = 0
    cardNum.eachWithIndex(){num, i -> 
        if(i%2==0) {
           ((num.toInteger()*2).toString().each(){snum -> total += snum.toInteger()})
        } else {
            total += num.toInteger()
        }
    }

    if(total%10==0)return 0
    else return 10 - (total%10)           
}

grandtotal = 0

limit = (10**xlen)-1
for (x in 0..limit){
    candidate = firstnum+String.format("%0${xlen}d", x)+lastnum
    if (luhn(candidate[0..-2]).toString()==candidate[-1]){
        grandtotal++
        //println candidate    
    }
}

println "Cards found: "+grandtotal