Codeforces Round #271 (Div. 2)D(递推，前缀和)

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<vector>
#include<algorithm>
#include<stack>
#include<queue>
#include<cctype>
#include<sstream>
using namespace std;
#define INF 1000000000
#define eps 1e-8
#define pii pair<int,int>
#define LL long long int
#define mod 1000000007
LL t,k,a,b,d[100010],s[100010];
int main()
{
    //freopen("in8.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    scanf("%I64d%I64d",&t,&k);
    for(int i=1;i<k;i++) d[i]=1;
    d[k]=2;
    for(int i=k+1;i<=100000;i++)
    {
        d[i]=(d[i-1]+d[i-k])%mod;
    }
    s[0]=0;
    s[1]=d[1];
    for(int i=2;i<=100000;i++)
    {
        s[i]=(s[i-1]+d[i])%mod;
    }
    for(int i=0;i<t;i++)
    {
        scanf("%I64d%I64d",&a,&b);
        printf("%I64d\n",(s[b]-s[a-1]+mod)%mod);
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}