将字符串“abc”全排列成：abc、acb、bac、bca、cab、cba

[STAThread]
static void Main()
{
string s = "abcd";
char[] add = s.ToCharArray();
pai(ref add, 0, s.Length);
Console.ReadKey();
}        //递归
private static void pai(ref char[] str, int m, int n)
{
if (m < n)
{
for (int i = 0; i <= m; i++)
{
pai(ref str, m + 1, n);
chang(ref str, m);
}
}
else
{
Console.WriteLine(str);
}
}
//移位
private static void chang(ref char[] str, int m)
{
char temp = str[0];
for (int i = 0; i < m; i++)
{
str[i] = str[i + 1];
}
str[m] = temp;
}