2902996_re.java

北大大牛代码 1240道题的原代码 超级权威

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

public class Main {
   
    static BigInteger one = new BigInteger ("1");
    
    public static BigInteger fact(BigInteger a)
    {
        if(a.intValue()==0||a.intValue()==1)
            return one;
        else
            return a.multiply(fact(a.subtract(one)));
    }
    
    public static void main(String[] args) throws Exception {
       
        Scanner cin = new Scanner (System.in);
        
        BigInteger p, q, r, s, t;
        int ans, tmp;
   
        while(cin.hasNext())
        {
            p = cin.nextBigInteger();
            q = cin.nextBigInteger();
            r = cin.nextBigInteger();
            s = cin.nextBigInteger();
            t = p.subtract(q);
            p = fact(p);
            q = fact(q);
            p = p.divide(q);
            if(t.intValue()!=0)
            {
                t = fact(t);
                p = p.divide(t);
            }
            t = r.subtract(s);
            r = fact(r);
            s = fact(s);
            
            r = r.divide(s);
            if(t.intValue()!=0)
            {
                t = fact(t);
                r = r.divide(t);
            }
            t = p.divide(r);
            ans = t.intValue();
            p = p.mod(r);
            p = p.multiply(new BigInteger("1000000"));
            p = p.divide(r);
            tmp = p.intValue();
            if(tmp%10>=5)
                tmp += 10;
            tmp /= 10;
            System.out.printf("%d.%05d\n",ans,tmp);
        }
    }
    
}