A. Points on Line

#include<stdio.h>
int main()
{
    int i,j,n,k,p;
    __int64 t=0,t1=0,a[100001]={1};
    scanf("%d %d",&n,&p);
    scanf("%I64d",&a[1]);
    for(i=2;i<=n;i++)
    {
        scanf("%I64d",&a[i]);
        while((a[i]-a[a[0]])>p)a[0]++;
        t+=((i-a[0])*(i-a[0]-1))/2;
    }
    printf("%I64d",t);
    return 0;
}

看代码长度  像一道水题。。

http://codeforces.com/contest/251/problem/A