题解

#include <iostream>
#include <algorithm>
using namespace std;
int n,b[200005],a,c;
int main(){
cin >> n >> c;
for(int i = 1;i <= n;i++){
cin >> b[i];
}
int cnt = 0;
sort(b+1,b+n+1);
for(int i = 1;i <= n;i++){
a = b[i] + c;
cnt += upper_bound(b+1,b+n+1,a) - lower_bound(b+1,b+n+1,a);
}
cout << cnt;
return 0;
}