python/TangDou/LuoGuBook/P1102.cpp

#include <bits/stdc++.h>

using namespace std;
const int N = 200010;
int a[N];
int c;
typedef long long LL;
LL cnt;

int main() {
    int n;
    cin >> n >> c;
    for (int i = 1; i <= n; i++) cin >> a[i];
    sort(a + 1, a + 1 + n);
    //遍历每一个数字
    for (int i = 1; i < n; i++) {
        int left = 0, right = 0;
        //左端点
        int l = 1, r = n, k = a[i] + c;
        while (l < r) {
            int mid = (l + r) >> 1;
            if (a[mid] >= k)r = mid;
            else l = mid + 1;
        }
        //也行找的到，也许找不到~
        if (a[l] == k)left = l;
        //右端点
        l = 1, r = n;
        while (l < r) {
            int mid = (l + r + 1) >> 1;
            if (a[mid] <= k)l = mid;
            else r = mid - 1;
        }
        //如果left存在，那么right也一定存在，大不了left=right嘛
        if (left) right = l;
        //左右端点差就是个数
        if (left) cnt += right - left + 1;//right==left,那就是1个
    }
    printf("%lld", cnt);
    return 0;
}