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

This is the a correct version which already examined by myself.

public static int Ackermann(int m, int n){
Stack s = new Stack;
s.add(m);
while(!s.isEmpty()){
    m=s.pop();
    if(m==0) { n+=m+1; }
    else if(n==0)
    {
       n += 1;
       s.add(--m);
    }
    else{
        s.add(--m);
        s.add(++m);
        n--;
    }
}
return n;
}