【BZOJ2348】[Baltic 2011]Plagiarism【二分】【或 Two Pointers】

【題目鏈接】

大水題竟然WA了2發。。

（1）二分找到位置後，貢獻應該是id - l...

（2）被卡精度了

/* Forgive me Not */
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

typedef long long LL;

const int maxn = 100005;

int n, num[maxn];

inline int iread() {
	int f = 1, x = 0; char ch = getchar();
	for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;
	for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
	return f * x;
}

inline int get(int id) {
	int l = 1, r = id - 1;
	while(l <= r) {
		int mid = l + r >> 1;
		if(num[mid] * 10 >= num[id] * 9) r = mid - 1;
		else l = mid + 1;
	}
	return id - l;
}

int main() {
	n = iread();
	for(int i = 1; i <= n; i++) num[i] = iread();
	sort(num + 1, num + 1 + n);

	LL ans = 0;
	for(int i = 1; i <= n; i++) ans += get(i);
	printf("%lld\n", ans);
	return 0;
}