How to rewrite Ackermann function in non-recursive style?

Question

I have function

public static int func(int M,int N){
    if(M == 0 || N == 0) return M+N+1;
    return func(M-1, func(M, N-1));
}

How to re

Answer 1

All the answers posted previously don't properly implement Ackermann.

def acker_mstack(m, n)
  stack = [m]
  until stack.empty?
    m = stack.pop

    if m.zero?
      n += 1
    elsif n.zero?
      stack << m - 1
      n = 1
    else
      stack << m - 1 << m
      n -= 1
    end
  end
  n
end