URAL 1036. Lucky Tickets java.math.BigInteger模板

状态转移方程：dp[ i ][ j ] = dp[ i ][ j ].add(dp[ i-1 ][ j-k ]);

比以前懒了。。。。贴个大数的模板留着以后用。

做DP的时候一定要找出状态转移方程的边界之后再开始敲哇。

import java.io.*;
import java.math.BigInteger;
import java.util.Scanner;
public class Main{  
    public static void main(String[] args) throws IOException{  
        Scanner cin = new Scanner(System.in);  
        int n, m, t; 
        n = cin.nextInt();   
        m = cin.nextInt();    

        BigInteger [][]dp = new BigInteger[100][1000];

        if(m%2 == 1 || m/2 > n*9)
        {
        	System.out.println("0");
        }
        else 
        {
        	for(int i = 0; i <= 50; ++i)
        	{
        		for(int j = 0; j <= 450; ++j)
        		{
        			dp[i][j] = BigInteger.ZERO;
        		}
        	}
        	m = m/2;
        	for(int i = 1; i <= 50; ++i)
        	{
        		dp[i][0] = BigInteger.ONE;
        	}
        	for(int i = 1; i <= 9; ++i)
        	{
        		dp[1][i] = BigInteger.ONE;
        	}
        	for(int i = 2; i <= n; ++i)
        	{
        		for(int j = i*9; j >= 1; --j)
        		{
        			for(int k = 0; j-k >= 0 && k <= 9; ++k)
        			{
        				dp[i][j] = dp[i][j].add(dp[i-1][j-k]);
        			}
        		}
        	}
        	System.out.println(dp[n][m].multiply(dp[n][m]));
        }
    }  
}