O(nlogn) map比数组好的是hash范围可以开到int 或者 ll 而数组则是2e7
但是复杂度略微高于手写hash
#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 10;
typedef long long ll;
int a[N], b[N];
int n, m;
map<int, int>h;
ll ans;
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> m;

    for(int i =1;i <= n;i++)cin >> a[i];

    sort(a + 1, a + 1 + n);

    int last = -1, cnt = 0;
    for(int i = 1;i <= n;i++)
    {
        if(a[i] != last){
            last = a[i];
            b[++cnt] = a[i];
        }
            h[a[i]] += 1;
    }
    //  for(int i = 1;i <= n;i++)cout << h[a[i]] << endl;

    for(int i = 1;i <= n;i++)
    {
        if(h[a[i] - m])
        {
            ans += h[a[i] - m];
        }
    }
    cout << ans;
}