gistfile1.groovy

final def KAPREKARS_CONSTANT = "6174"
final def MAX_ITERATIONS = 7

def startingDigits = "1123"
def iterations = 0
def solved = false

println "Attempting to solve ${startingDigits}:"

for(res = startingDigits; iterations < MAX_ITERATIONS && !solved; iterations++) {
    res = res.toList().sort()
    def a = res.reverse().join().toInteger()
    def b = res.join().toInteger()

    res = (a - b).toString().padLeft(4, '0')
    println "${iterations+1}. ${a} - ${b} = ${res}"
    solved = (res == KAPREKARS_CONSTANT)
}

println ""
if(solved)
    println "Solved within ${iterations} iterations."
else
    println "Unable to solve."