POJ - 1737 Connected Graph，Java（计数类DP）

POJ - 1737 Connected Graph

C++高精太难写了，直接用Java的大整数会方便一点

常规方法

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

public class Main {
    static Scanner cin = new Scanner(System.in);
    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    public static BigInteger ksm(int k)
    {
        BigInteger res=BigInteger.ONE;
        for(int i=1;i<=k*(k-1)/2;i++) res=res.multiply(BigInteger.valueOf(2));
        return res;
    }
    public static BigInteger C(int a,int b)
    {
        BigInteger res=BigInteger.ONE;
        for(int i=1;i<=a;i++) res=res.multiply(BigInteger.valueOf(i));
        for(int i=1;i<=b;i++) res=res.divide(BigInteger.valueOf(i));
        for(int i=1;i<=a-b;i++) res=res.divide(BigInteger.valueOf(i));
        return res;
    }
    public static void main(String[] args) throws IOException{
        while(cin.hasNext())
        {
            int n=cin.nextInt();
            if(n==0) break;
            BigInteger []f = new BigInteger[n+1];
            f[1]=BigInteger.ONE;
            for(int i=1;i<=n;i++)
            {
                f[i]=ksm(i);
                for(int j=1;j<i;j++)
                    f[i]=f[i].subtract(f[j].multiply(C(i-1,i-j).multiply(ksm(i-j))));
            }
            bw.write(f[n].toString()+"\n");
        }
        bw.flush();
    }
}

预处理50种情况

import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Scanner;
public class Main {
    static Scanner cin = new Scanner(System.in);
    static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
    public static BigInteger ksm(int k)
    {
        BigInteger res=BigInteger.ONE;
        for(int i=1;i<=k*(k-1)/2;i++) res=res.multiply(BigInteger.valueOf(2));
        return res;
    }
    public static BigInteger C(int a,int b)
    {
        BigInteger res=BigInteger.ONE;
        for(int i=1;i<=a;i++) res=res.multiply(BigInteger.valueOf(i));
        for(int i=1;i<=b;i++) res=res.divide(BigInteger.valueOf(i));
        for(int i=1;i<=a-b;i++) res=res.divide(BigInteger.valueOf(i));
        return res;
    }
    public static void main(String[] args) {
        BigInteger [][]f = new BigInteger[51][51];
        for(int k=1;k<=50;k++)
        {
            f[k][1]=BigInteger.ONE;
            for(int i=1;i<=k;i++)
            {
                f[k][i]=ksm(i);
                for(int j=1;j<i;j++)
                    f[k][i]=f[k][i].subtract(f[k][j].multiply(C(i-1,i-j).multiply(ksm(i-j))));
            }
        }
        while(cin.hasNext())
        {
            int n=cin.nextInt();
            if(n==0) break;
            out.println(f[n][n]);
        }
        out.flush();
    }
}