递推DP URAL 1225 Flags

 

题目传送门

 1 /*
 2     1 r; 2 b; 3 w
 3     2不能在最前面，所以dp[1] = 2;    dp[2] = 2: 13 or 31
 4 
 5     dp[i] = dp[i-1] + dp[i-2];
 6     只加1或3时，总数dp[i-1];    只加12或32时，总数dp[i-2];
 7     详细解释：http://www.cnblogs.com/vongang/archive/2011/09/30/2196847.html
 8 */
 9 #include <cstdio>
10 #include <iostream>
11 #include <algorithm>
12 #include <cstring>
13 using namespace std;
14 
15 const int MAXN = 55;
16 const int INF = 0x3f3f3f3f;
17 long long dp[MAXN];
18 
19 int main(void)        //URAL 1225 Flags
20 {
21     //freopen ("A.in", "r", stdin);
22 
23     int n;
24     while (scanf ("%d", &n) == 1)
25     {
26         memset (dp, 0, sizeof (dp));
27 
28         dp[1] = 2;    dp[2] = 2;
29         for (int i=3; i<=n; ++i)
30         {
31             dp[i] = dp[i-1] + dp[i-2];
32         }
33 
34         printf ("%I64d\n", dp[n]);
35     }
36 
37     return 0;
38 }

 

posted @ 2015-05-06 17:37  Running_Time  阅读(167)  评论(0)  编辑  收藏  举报