HDU 2047 EOF牛肉串

水到不想整理，线性DP

 #include <algorithm>
 #include <iostream>
 #include <cstring>
 #include <cstdio>

 using namespace std;

 long long n, dp[][], ans = ;

 int main()
 {
     while (~scanf("%d", &n))
     {
         ans = ;
         if (n == ) { puts(""); continue; }
         memset(dp, , sizeof(dp));
         dp[][] = dp[][] = dp[][] = ;
         for (int i = ; i <= n; ++i)
             dp[i][] = dp[i - ][] + dp[i - ][],
             dp[i][] = dp[i - ][] + dp[i - ][] + dp[i - ][],
             dp[i][] = dp[i - ][] + dp[i - ][] + dp[i - ][];
         printf("%lld\n", dp[n][] + dp[n][] + dp[n][]);
     }
     return ;
 }