C# 简单的统计指定几个字符组合的所有结果

private string[] AAA()
{
string[] cs = { "a", "b", "c", "d" };
string[] ts = new string[8];
string[] ss = new string[Convert.ToInt32(Math.Pow(cs.Length, 8))];
int index = 0;
for (int i_0 = 0; i_0 < cs.Length; i_0++)
{
for (int i_1 = 0; i_1 < cs.Length; i_1++)
{
for (int i_2 = 0; i_2 < cs.Length; i_2++)
{
for (int i_3 = 0; i_3 < cs.Length; i_3++)
{
for (int i_4 = 0; i_4 < cs.Length; i_4++)
{
for (int i_5 = 0; i_5 < cs.Length; i_5++)
{
for (int i_6 = 0; i_6 < cs.Length; i_6++)
{
for (int i_7 = 0; i_7 < cs.Length; i_7++)
{
ts[0] = cs[i_0];
ts[1] = cs[i_1];
ts[2] = cs[i_2];
ts[3] = cs[i_3];
ts[4] = cs[i_4];
ts[5] = cs[i_5];
ts[6] = cs[i_6];
ts[7] = cs[i_7];
ss[index++] = String.Join("-", ts);
}
}
}
}
}
}
}
}
return ss;
}

private string[] BBB()
{
string[] cs = { "a", "b", "c", "d" };
int power = 8;
string[] ss = new string[Convert.ToInt32(Math.Pow(cs.Length, power))];
string[] ts = new string[power];
int i = 0;
int index = 0;
Recur(cs, ref i, power - 1, ts, ref index, ss);
return ss;
}

private void Recur(string[] cs, ref int i, int power, string[] ts, ref int index, string[] ss)
{
for (int j = 0; j < cs.Length; j++)
{
ts[i] = cs[j];
if (i < power)
{
i++;
Recur(cs, ref i, power, ts, ref index, ss);
}
else
{
ss[index++] = String.Join("-", ts);
}
}
i--;
}