洛谷1102（尺取）

P1102 A-B 数对 - 洛谷 | 计算机科学教育新生态

#include<iostream>
#include<algorithm>
using namespace std;
const int N = 2e5 + 5;
int a[N];
int main() {
	__int64 n, t, res = 0;
	cin >> n >> t;
	for (int i = 1; i <= n; i++) { cin >> a[i]; }
	sort(a + 1, a + 1 + n);
	for (int i = 1, j = 1, k = 1; i <= n; i++) {
		while (j <= n && a[j] - a[i] < t) { j++; }
		while (k <= n && a[k] - a[i] <= t) { k++; }
		if (a[j] - a[i] == t && a[k - 1] - a[i] == t && k - 1 >= 1) {
			res += k - j;
		}
	}
	cout << res;
	return 0;
}