bzoj1878 [SDOI2009]HH的项链【莫队】

传送门：http://www.lydsy.com/JudgeOnline/problem.php?id=1878

以每个询问左端点所属的块的编号为第一关键字，右端点本身为第二关键字，排序，然后保利扫描，先移动右指针。

（逻辑相等号写成赋值号，调了1个小时，天呐，上次犯这个错误是多久以前了呀？）

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

const int maxn = 50005, maxm = 200005;

int n, m, a[maxn], ans[maxm], siz, ima, left, right, book[1000005];
struct query {
	int l, r, id;
} b[maxm];

bool cmp(const query & aa, const query & ss) {
	if (aa.l / siz == ss.l / siz) {
		return aa.r < ss.r;
	}
	return aa.l / siz < ss.l / siz;
}

int main(void) {
	//freopen("in.txt", "r", stdin);
	//freopen("out.txt", "w", stdout);
	scanf("%d", &n);
	siz = (int)sqrt((float)n + 0.5f);
	for (int i = 1; i <= n; ++i) {
		scanf("%d", a + i);
	}
	scanf("%d", &m);
	for (int i = 1; i <= m; ++i) {
		scanf("%d%d", &b[i].l, &b[i].r);
		b[i].id = i;
	}
	std::sort(b + 1, b + m + 1, cmp);
	
	//a[0] = 1000003;
	book[a[0]] = 1;
	ima = 1;
	for (int i = 1; i <= m; ++i) {
		while (right < b[i].r) {
			++right;
			if (++book[a[right]] == 1) {
				++ima;
			}
		}
		while (right > b[i].r) {
			if (--book[a[right]] == 0) {
				--ima;
			}
			--right;
		}
		while (left < b[i].l) {
			if (--book[a[left]] == 0) {
				--ima;
			}
			++left;
		}
		while (left > b[i].l) {
			--left;
			if (++book[a[left]] == 1) {
				++ima;
			}
		}
		ans[b[i].id] = ima;
	}
	
	for (int i = 1; i <= m; ++i) {
		printf("%d\n", ans[i]);
	}
	return 0;
}