直接二分（doge）（其实是懒得处理重复的问题doge）

#include<bits/stdc++.h>
#define M 200010
using namespace std;
int n,c;
long long ans=0;
int num[M];
int main(){
	scanf("%d %d",&n,&c);
	for(int i=0;i<n;++i) scanf("%d",&num[i]);
	sort(num,num+n);
	int mid=0;
	for(int i=n-1;i>=0;--i){
		int l=0,r=n-1;
		while(l<=r){
			mid=(l+r)>>1;
			if(num[i]-num[mid]>c)l=mid+1;
			else r=mid-1;
		}
		int nmid,ll=0,rr=n-1;
		while(ll<=rr){
			nmid=ll+((rr-ll)>>1);
			if(num[i]-num[nmid]<c)rr=nmid-1;
			else ll=nmid+1;
		}
		ans+=ll-l;
	}
	printf("%lld",ans);
	return 0;
}