A Groovy solution for Project Euler - Problem 3

euler3.groovy

def largestPrimeFactorOf = { BigInteger it, divisor = 1, factors = [] ->
  while (it > 1) { 
    divisor += 1
    while (it % divisor == 0) { 
      factors << divisor
      it /= divisor
    }
  }
  factors.last()
}

assert largestPrimeFactorOf(600851475143) == 6857