URAL 1225 Flags dp练习

On the Day of the Flag of Russia a shop-owner decided to decorate the show-window of his shop with textile stripes of white, blue and red colors. He wants to satisfy the following conditions:
Stripes of the same color cannot be placed next to each other.
A blue stripe must always be placed between a white and a red or between a red and a white one.

Determine the number of the ways to fulfill his wish.

Example. For N = 3 result is following:



对于此题有题目给出的条件很容易确定状态方程  对于已经有N个块且最后为白的状态 dp
[0];
1 如果后面加上红色块
                                     dp[N+1][1] += dp
[0];
2 后面加上蓝色块，则蓝色后要补上红色
                                     dp[N+2][1] +=dp
[0];

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;
ll dp[50][2];
int main()
{
dp[1][0] = 1;
dp[1][1] = 1;
for(int i = 2; i <= 45; i++) dp[i][1] = dp[i][0] = 0;
for(int i = 1; i <= 45; i++)
{
dp[i+1][1] += dp[i][0];
dp[i+1][0] += dp[i][1];
dp[i+2][1] += dp[i][0];
dp[i+2][0] += dp[i][1];
}
int n;
while(scanf("%d",&n)!=EOF)
{
printf("%I64d\n",dp
[0]+dp
[1]);
}
return 0;
}