牛客2018年第二次多校培训----A-run

题目描述：

链接：https://www.nowcoder.com/acm/contest/140/A
来源：牛客网

时间限制：C/C++ 1秒，其他语言2秒
空间限制：C/C++ 131072K，其他语言262144K
64bit IO Format: %lld

题目描述

White Cloud is exercising in the playground.
White Cloud can walk 1 meters or run k meters per second.
Since White Cloud is tired,it can't run for two or more continuous seconds.
White Cloud will move L to R meters. It wants to know how many different ways there are to achieve its goal.
Two ways are different if and only if they move different meters or spend different seconds or in one second, one of them walks and the other runs.

输入描述:

The first line of input contains 2 integers Q and k.Q is the number of queries.(Q<=100000,2<=k<=100000)
For the next Q lines,each line contains two integers L and R.(1<=L<=R<=100000)

输出描述:

For each query,print a line which contains an integer,denoting the answer of the query modulo 1000000007.

示例1

输入

3 3
3 3
1 4
1 5

输出

2
7
11

#include <iostream>
#include <stdio.h>
#define MOD 1000000007
using namespace std;
int main()
{
    long long a[100005],b[100005];
    int q,k,l,r;
    cin>>q>>k;
    b[0]=0;
    for(int i=1;i<k;i++)
    {
        a[i]=1;
        b[i]=b[i-1]+a[i];
    }
    a[k]=2;b[k]=b[k-1]+a[k];
    a[k+1]=3;b[k+1]=b[k]+a[k+1];
    for(int i=k+2;i<100005;i++)
    {
        a[i]=(a[i-1]+a[i-k-1])%MOD;
        b[i]=(b[i-1]+a[i])%MOD;
    }
    for(int i=0;i<q;i++)
    {
        cin>>l>>r;
        printf("%lld
",(MOD+b[r]-b[l-1])%MOD);
    }
    return 0;
}