アッカーマン関数続

インデックスを一つの構造体で管理するようにしてすっきりした。

struct index2D
{
    public int m, n;
    public override int GetHashCode()
    {
        return m ^ n;
    }
}
static Dictionary<index2D, int> Ack = new Dictionary<index2D, int>();
static int Ackermann(index2D mn)
{
    System.Diagnostics.Stopwatch watch = new System.Diagnostics.Stopwatch();
    watch.Start();
    Stack<index2D> arg = new Stack<index2D>();
    arg.Clear();
    arg.Push(mn);
    while (arg.Count > 0) {
        index2D index = arg.Peek();
        index2D index_;
        if (Ack.ContainsKey(index)) {
            arg.Pop();
            continue;
        } else {
            int value;
            if (index.m == 0) {
                value = checked(arg.Peek().n + 1);
            } else if (index.n == 0) {
                index_.m = index.m - 1;
                index_.n = 1;
                if (Ack.ContainsKey(index_)) {
                    value = Ack[index_];
                } else {
                    arg.Push(index_);
                    continue;
                }
            } else {
                index_.m = index.m;
                index_.n = index.n - 1;
                int n_;
                if (Ack.ContainsKey(index_)) {
                    n_ = Ack[index_];
                } else {
                    arg.Push(index_);
                    continue;
                }
                index_.m = index.m - 1;
                index_.n = n_;
                if (Ack.ContainsKey(index_)) {
                    value = Ack[index_];
                } else {
                    arg.Push(index_);
                    continue;
                 }
            }
            Ack[index] = value;
            continue;
        }
    }
    watch.Stop();
    Console.WriteLine(watch.Elapsed.ToString() + " elapsed.");
    return Ack[mn];
}