luoguP1102-双指针

#include <bits/stdc++.h>

using namespace std;

const int N = 2 * 1e5 + 10;

typedef long long LL;

int n, c, s[N];
LL sum;

int main()
{
    cin >> n >> c;
    for(int i = 0; i < n; ++ i) cin >> s[i];

    sort(s, s + n);

    int l = 0, r = 0;
    for(int i = 0; i < n; ++ i) {
        while(s[l] < s[i] - c && l < n) ++ l;/
        while(s[r] <= s[i] - c && r < n) ++ r; 
        if(s[i] - s[l] == c) sum += r - l;
    }
    cout << sum << endl;
    return 0;
}