快排+二分 #101112RE求调TOT

#include <stdio.h>
#include <time.h>
#include <stdlib.h>
long long int a[20005];
int n;
void swap(long long int*a,long long int *b)
{
	long long int temp=*a;
	*a=*b;
	*b=temp;
}
void qs(int l,int r)
{
	if(l>=r) return;
	int p=a[l+(rand())%(r-l)];
	int lf=l,rt=r,i=l;
	while(i<=rt)
	{
		if(a[i]<p) swap(&a[i++],&a[lf++]);
		else if(a[i]>p) swap(&a[i],&a[rt--]);
		else i++;
	}
	qs(l,lf-1);
	qs(rt+1,r);
}
int find_lower(long long int x)
{
	int lf=1,rt=n+1;
	while(lf<rt)
	{
		int mid=(lf+rt)>>1;
		if(a[mid]<x) lf=mid+1;
		else rt=mid;
	}
	return (lf<=n&&a[lf]==x) ? lf:-1;
}
int find_upper(long long int x)
{
	int lf=1,rt=n+1;
	while(lf<rt)
	{
		int mid=(lf+rt+1)>>1;
		if(a[mid]<=x) lf=mid;
		else rt=mid-1;
	}
	return (a[lf]==x) ? lf:-1;
}
int main()
{
	srand((unsigned)time(NULL));
	long long int b,ans=0;
	scanf("%d%lld",&n,&b);
	for (int i=1;i<=n;i++)
	{
		scanf("%lld",&a[i]);
	}	
	qs(1,n);
	for (int i=1;i<=n;i++)
	{
		if(find_upper(a[i]-b)!=-1&&find_lower(a[i]-b)!=-1)ans+=(find_upper(a[i]-b)-find_lower(a[i]-b)+1);
	}
	printf("%lld",ans);
    return 0;
}