public static void Unrank(int n, long r, int[] pi)
{
if (n == 1)
{
return;
}
int s = (int)(r / KevinMath.Factorial(n - 1));
ArrayUtility.Swap(pi, n - 1, s);
Unrank(n - 1, r % KevinMath.Factorial(n - 1), pi);
}
public static long Rank(int n, int[] pi, int[] inv)
{
if (n == 1)
{
return(0);
}
int s = pi[n - 1];
ArrayUtility.Swap(pi, n - 1, inv[n - 1]);
ArrayUtility.Swap(inv, s, inv[n - 1]);
return(s * KevinMath.Factorial(n - 1) + Rank(n - 1, pi, inv));
}
public void UnrankSingletonString()
{
string s = "x";
int n = s.Length;
long r = KevinMath.LongRandom(0, KevinMath.Factorial(n) - 1, new Random());
int[] pi = RankUnrank.InitIndexArray(n);
RankUnrank.Unrank(n, r, pi);
string ps = GetPermString(s, pi);
Console.WriteLine(string.Format("r:{0} s:{1} p:{2}", r, s, ps));
}
public void UnrankStringLenThree()
{
string s = "xyz";
int n = s.Length;
Console.WriteLine(string.Format("s:{0}", s));
for (int r = 0; r < KevinMath.Factorial(n); r++)
{
int[] pi = RankUnrank.InitIndexArray(n);
RankUnrank.Unrank(n, r, pi);
string ps = GetPermString(s, pi);
Console.WriteLine(string.Format("r:{0} p:{1}", r, ps));
//int[] inv = RankUnrank.GetInverseArray(pi);
//long rank = RankUnrank.Rank(n, pi, inv);
//Assert.AreEqual(r, rank);
}
}