Ackermann function

gistfile1.cpp

#include <iostream>
#include <stack>
#include <cstdlib>

typedef unsigned long long ull;

ull ack(ull m, ull n)
{
    std::stack<ull> st;
    st.push(m);

    while (!st.empty())
    {
        if (st.top() == 0)
        {
            st.pop();
            n++;
        }
        else if (n == 0)
        {
            m = st.top();
            st.pop();
            st.push(m - 1);
            n = 1;
        }
        else
        {
            m = st.top();
            st.pop();
            st.push(m - 1);
            st.push(m);
            n--;
        }
    }

    return n;
}

int main(int argc, char **argv)
{
    ull m = std::atoll(argv[1]);
    ull n = std::atoll(argv[2]);

    std::cout << "ack(" << m << ", " << n << ") = " << ack(m,n) << std::endl;

    return 0;
}