Generate n unique random natural numbers whose sum is m

random_sum.rb

# Question source: http://codegolf.stackexchange.com/q/8574/12268

# Write an algorithm in any programming language you desire
# that generates n unique randomly-distributed random natural
# numbers (i.e. positive integers, no zero), sum of which is
# equal to t, where t is bigger than or equal to n*(n+1)/2.

# Example: Generate 10 unique random natural numbers, sum of which is equal to 500.

def rand_sum(size, sum)
  rand_set = [] 
  rand_set |= [rand(1...sum)] until rand_set.size == size - 1
  rand_set << 0 << sum
  rand_set = rand_set.sort.each_cons(2).map { |x, y| y - x }.uniq
  rand_set.size == size ? rand_set : rand_sum(size, sum)
end