hdu 1143 Tri Tiling

题目：hdu 1143 Tri Tiling

思路：dp[i]=3*dp[i-3]+2*(dp[i-4]+dp[i-6]+...+dp[2]+dp[0]);

 

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Scanner;

public class Main
{
    public static void main(String args[])
    {
        Scanner cin=new Scanner(System.in);
        long dp[]=new long[31];
        long sum[]=new long[31];
        dp[0]=1;
        dp[1]=0;
        dp[2]=3;
        dp[3]=0;
        sum[0]=1;
        sum[2]=4;
        for(int i=4;i<31;i++)
        {
             dp[i]=3*dp[i-2]+2*sum[i-4];
             if(i%2==0)
                 sum[i]=dp[i]+sum[i-2];
        }
        while(cin.hasNext())
        {
            int n=cin.nextInt();
            if(n==-1)
                break;
            System.out.println(dp[n]);
        }
    }

}