Problem Statement

(Given an equal-probability generator of one of the integers 1 to 5 as dice5),   create dice7 that generates a pseudo-random integer from 1 to 7 in equal probability using only dice5 as a source of random numbers,   and check the distribution for at least one million calls using the function created in   Simple Random Distribution Checker.

Implementation suggestion: dice7 might call dice5 twice, re-call if four of the 25 combinations are given, otherwise split the other 21 combinations into 7 groups of three, and return the group index from the rolls. (Task adapted from an answer here)

Let's start with the solution:

def dice5() {
  return entropy.nextInt(5) + 1
}

def dice7() {
  var d55 := null
  while ((d55 := 5 * dice5() + dice5() - 6) >= 21) {}
  return d55 %% 7 + 1
}

def bins := ([0] * 7).diverge()
for x in 1..1000 {
  bins[dice7() - 1] += 1
}
println(bins.snapshot())