BZOJ 2013 : [Ceoi2010]A huge tower / Luogu SP6950 CTOI10D3 - A HUGE TOWER

传送门

菜鸡.jpg

CODE

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 620005;
int n, d, a[MAXN];
int main() {
	scanf("%d%d", &n, &d);
	for(int i = 1; i <= n; ++i)
		scanf("%d", &a[i]);
	sort(a + 1, a + n + 1);
	int pt = 1, ans = 1;
	for(int i = 2; i <= n; ++i) {
		while(pt <= n && a[pt]+d < a[i]) ++pt;
		ans = 1ll * ans * (i-pt+1) % 1000000009;
	}
	printf("%d\n", ans);
}