_bzoj2038 [2009国家集训队]小Z的袜子(hose)【莫队】

#include <cstdio>
#include <algorithm>
#include <cmath>

const int maxn = 50005, maxm = 50005;

int n, m, c[maxn], s[maxn], l, r, siz;
long long fenzi[maxm], fenmu[maxm], tem, same;
struct st {
	int l, r;
	int id;
} q[maxm];

bool cmp(const st & aa, const st & ss) {
	if (aa.l / siz == ss.l / siz) {
		return aa.r < ss.r;
	}
	return aa.l / siz < ss.l / siz;
}
inline long long gcd(long long aa, long long ss) {
	long long tt;
	while (ss) {
		tt = aa;
		aa = ss;
		ss = tt % ss;
	}
	return aa;
}

int main(void) {
	//freopen("in.txt", "r", stdin);
	scanf("%d%d", &n, &m);
	siz = (int)sqrt((float)n + 0.5f);
	for (int i = 1; i <= n; ++i) {
		scanf("%d", c + i);
	}
	for (int i = 1; i <= m; ++i) {
		scanf("%d%d", &q[i].l, &q[i].r);
		q[i].id = i;
	}
	std::sort(q + 1, q + m + 1, cmp);
	
	for (int i = q[1].l; i <= q[1].r; ++i) {
		++s[c[i]];
	}
	for (int i = 0; i <= n; ++i) {
		same += (long long)s[i] * (long long)(s[i] - 1) >> 1;
	}
	l = q[1].l;
	r = q[1].r;
	fenmu[q[1].id] = (long long)(q[1].r - q[1].l + 1) * (long long)(q[1].r - q[1].l) >> 1;
	fenzi[q[1].id] = same;
	tem = gcd(fenmu[q[1].id], fenzi[q[1].id]);
	fenmu[q[1].id] /= tem;
	fenzi[q[1].id] /= tem;
	for (int i = 2; i <= m; ++i) {
		fenmu[q[i].id] = (long long)(q[i].r - q[i].l + 1) * (long long)(q[i].r - q[i].l) >> 1;
		while (r < q[i].r) {
			++r;
			same += s[c[r]];
			++s[c[r]];
		}
		while (r > q[i].r) {
			same += 1 - s[c[r]];
			--s[c[r]];
			--r;
		}
		while (l > q[i].l) {
			--l;
			same += s[c[l]];
			++s[c[l]];
		}
		while (l < q[i].l) {
			same += 1 - s[c[l]];
			--s[c[l]];
			++l;
		}
		fenzi[q[i].id] = same;
		tem = gcd(fenmu[q[i].id], fenzi[q[i].id]);
		fenmu[q[i].id] /= tem;
		fenzi[q[i].id] /= tem;
	}
	for (int i = 1; i <= m; ++i) {
		printf("%lld/%lld\n", fenzi[i], fenmu[i]);
	}
	return 0;
}