2019.2.14 t2 程序调试

代码：

 #include <cstdio>
 #include <iostream>
 #include <cstring>
 #include <algorithm>
 #include <cmath>
 #include <cctype>
 using namespace std;

 #define LL long long
 #define res register int

 const int N=+,mod=1e9+;
 int f[N],n,k;

 int main()
 {
     freopen("debug.in","r",stdin);
     freopen("debug.out","w",stdout);
     scanf("%lld %lld",&n,&k);
     f[]=;
     for(res i= ; i<=n ; i++)
     {
         f[i]=f[i-];
         if(i>=k) f[i]=(f[i]+f[i-k])%mod;
         else f[i]=(f[i]+)%mod;
     }
     if(n-2k+<) ans=(f[n-k]-)%mod;
     int ans=(f[n-k]+(LL)k*f[n-*k+]%mod-)%mod;
     printf("%d\n",ans);
     return ;
 }