莫队模板

#include<bits/stdc++.h>

using namespace std;

using i64 = long long;

const int N = 1e6 + 5;
int cnt[N], a[N];

struct query {
    int l, r, id;
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n;
    cin >> n;

    int M = sqrt(n);

    for (int i = 1; i <= n; i ++)
        cin >> a[i];

    int m;
    cin >> m;
    vector<query> q(m);
    for (int i = 0; i < m; i ++) {
        int l, r;
        cin >> l >> r;
        q[i] = {l, r, i};
    }
	//按分块大小排序，在同一个块的按块的奇偶性将右端点正序或逆序排序
    sort(q.begin(), q.end(), [&M](query x, query y) {
        return (((x.l / M) ^ (y.l / M)) ? x.l < y.l : ((x.l / M) & 1) ? x.r<y.r: x.r>y.r);
    });

    int l = 1, r = 0, now = 0;
    vector<int> ans(m);
    for (int i = 0; i < m; i ++) {
        auto [ql, qr, id] = q[i];
		//易错点
        while (l < ql)  now -= !--cnt[a[l++]];
        while (l > ql) now += !cnt[a[--l]]++;
        while (r < qr) now += !cnt[a[++r]]++;
        while (r > qr) now -= !--cnt[a[r--]];

        ans[id] = now;
    }

    for (int i = 0; i < m; i ++)
        cout << ans[i] << "\n";

    return 0;
}