请教一个简单的数字组合问题

             ArrayList list = new ArrayList();
            int[] data = { 1, 2, 3, 4 };
            int m = 3;
            if (m == 1)
            {
                foreach (int n in data)
                {
                    list.Add(n);
                }
            }
            if (m == 2)
            {
                foreach (int n1 in data)
                {
                    foreach (int n2 in data)
                    {
                        if(n1!=n2 && n1<n2)
                        {
                          string s = n1.ToString()+n2.ToString();
                          list.Add(s);
                        }
                    }
                }
            }
            if (m == 3)
            {
                foreach (int n1 in data)
                {
                    foreach (int n2 in data)
                    {
                        foreach (int n3 in data)
                        {
                            if (n1 != n2 && n1!=n3 && n2!=n3&& n1<n2&& n2<n3 )
                            {
                                string s = n1.ToString() + n2.ToString()+n3.ToString();
                                list.Add(s);
                            }
                        }
                    }
                }
            }
            if (m == 4)
            {
                string s = string.Empty;
                foreach (int n in data)
                { 
                     s=s+n.ToString();
                }
                list.Add(s);
            }