Codeforces 474D Flowers

http://codeforces.com/problemset/problem/474/D

思路:F[i]=F[i-1]+(i>=K)F[i-k]

 #include<cstdio>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<iostream>
 const int Mod=;
 int K,sum[],f[];
 int read(){
     int t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 void init(){
     f[]=;
     for (int i=;i<=;i++){
      f[i]=(f[i-])%Mod;
      if (i>=K)
       f[i]=(f[i]+f[i-K])%Mod;
     }
     for (int i=;i<=;i++)
      sum[i]=(sum[i-]+f[i])%Mod;
 }
 int main(){
     int T=read();K=read();
     init();
     while (T--){
         int l=read(),r=read();
         printf("%d\n",((sum[r]-sum[l-])%Mod+Mod)%Mod);
     }
     return ;
 }