poj3226

高精度组合数学

View Code

import java.io.*;
import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) throws FileNotFoundException
    {
        Scanner cin = new Scanner(new BufferedInputStream(System.in));
        //Scanner cin = new Scanner(new FileInputStream("t.txt"));
        int n = cin.nextInt();
        while (n != 0)
        {
            String st = cin.next();
            BigInteger a = new BigInteger("1");
            BigInteger ans = new BigInteger("0");
            int[] f = new int[30];
            for (int i = 0; i < n; i++)
                f[i] = st.charAt(i) - 'A';
            for (int i = n - 1; i >= 0; i--)
            {
                int x = 0;
                for (int j = 0; j < i; j++)
                    if (f[j] < f[i])
                        x++;
                f[i] -= x;
            }
            for (int i = n - 1; i >= 0; i--)
            {
                int x = f[i];
                ans = ans.add(BigInteger.valueOf(x).multiply(a));
                a = a.multiply(BigInteger.valueOf(26 - i));
            }
            System.out.println(ans);
            n = cin.nextInt();
        }
    }
}