def top_sort_it():


    for n in nodes:

        if n is not in visited:
            stack.push(n)

        while stack is not empty:
            candidate = stack.top
            last = True

            for x in candidate.nodes:
                if x is not in visited:
                    visited.insert(x)
                    last = False
                    stack.push(x)

            if last is True:
                save(candidate)
                stack.pop()


1   ->  2
3   ->  2  -> 4


n = 2           stack: 2
candidate = 2   last = True
stack: 2 4      last = False
candidate = 4   last = True
save(4)         stack: 2

candidate = 2   last = True
save(2)         stack: