H - Points on Line

#include<stdio.h>
#include<algorithm>
using namespace std;
typedef long long LL;
const int N=1e5+5;
int a[N],n,k;
LL tmp,ans;
int main()
{
    while(~scanf("%d%d",&n,&k))
    {
        ans=0;
        for(int i=0;i<n;i++)
            scanf("%d",&a[i]);
        for(int i=0;i<n-2;i++)
        {
            tmp=upper_bound(a+i,a+n,a[i]+k)-a-i-1;
            ans+=tmp*(tmp-1)/2;
        }
        printf("%lld\n",ans);
    }
}

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define maxn 100050
ll ans,n,k,a[maxn];
int main()
{
    scanf("%lld%lld",&n,&k);
    for(int i=0; i<n; i++)
        scanf("%lld",&a[i]);
    ll head=0,tail=2;
    while(tail<n)
    {
        while(tail<n&&a[tail]-a[head]<=k)
        {
            ans+=(tail-head)*(tail-head-1)/2;
            tail++;
        }
        if(tail==n)break;
        while(a[tail]-a[head]>k)head++;
    }
    printf("%lld\n",ans);
}