[洛谷P1972][SDOI2009]HH的项链

题目大意：给你一串数字，多次询问区间内数字的种类数

题解：莫队

卡点：洛谷数据加强，开了个$O(2)$

C++ Code：

#include <cstdio>
#include <algorithm>
#define bsz 710
#define maxn 500010
#define N 1000010
int ans[maxn];
int n, m;
int s[maxn], cnt[N];
struct Query {
	int l, r, pos;
	inline bool operator < (const Query &rhs) const {return l / bsz == rhs.l / bsz ? (l / bsz & 1 ? r < rhs.r : r > rhs.r) : l < rhs.l;}
} q[maxn];
int main() {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++) scanf("%d", s + i);
	scanf("%d", &m);
	for (int i = 1; i <= m; i++) {
		scanf("%d%d", &q[i].l, &q[i].r);
		q[i].pos = i;
	}
	std::sort(q + 1, q + m + 1);
	int l = 1, r = 1, res = 1; cnt[s[1]]++;
	for (int i = 1; i <= m; i++) {
		while (l > q[i].l) cnt[s[--l]]++ ? 0 : res++;
		while (r < q[i].r) cnt[s[++r]]++ ? 0 : res++;
		while (l < q[i].l) --cnt[s[l++]] ? 0 : res--;
		while (r > q[i].r) --cnt[s[r--]] ? 0 : res--;
		ans[q[i].pos] = res;
	}
	for (int i = 1; i <= m; i++) printf("%d\n", ans[i]);
	return 0;
}