Painting Storages（ZOJ)

There is a straight highway with N storages alongside it labeled by 1,2,3,...,N. Bob asks you to paint all storages with two colors: red and blue. Each storage will be painted with exactly one color.

Bob has a requirement: there are at least M continuous storages (e.g. "2,3,4" are 3 continuous storages) to be painted with red. How many ways can you paint all storages under Bob's requirement?

Input

There are multiple test cases.

Each test case consists a single line with two integers: N and M (0

Process to the end of input.

Output

One line for each case. Output the number of ways module 1000000007.

Sample Input

4 3 

Sample Output

3

 1 #include 
 2 #include <string.h>
 3 const int N = 1e5 + 5;
 4 const int mod = 1e9 + 7;
 5 int dp[N],pow[N]= {1};
 6 
 7 int main()
 8 {
 9     int n,m;
10     for(int i=1; i1] * 2 % mod;
11     while(~scanf("%d%d",&n,&m))
12     {
13         memset(dp,0,sizeof(int)*m);
14         dp[m] = 1;
15         for(int i=m+1; i<=n; i++) dp[i] = ((dp[i-1]*2 % mod + pow[i-m-1]-dp[i-m-1]) % mod + mod) % mod;
16         printf("%d\n",dp[n]);
17     }
18     return 0;
19 }

数论（排列组合）

 

转载于:https://www.cnblogs.com/contestant/p/3239592.html