Distinct Values Queries

                                #include <bits/stdc++.h>

using namespace std;

const int MX = 4e5 + 5;

int bit[MX];
int n, q, sol[MX];
vector<pair<int, int>> query[MX];
vector<int> x(MX);
map<int, int> fst;

int qry (int i) {
	int res = 0;
	for (; i; i -= i&(-i)) {
		res += bit[i];
	}
	return res;
}

void upd (int i, int val) {
	for (; i <= n; i += i&(-i)) {
		bit[i] += val;
	}
}

int main () {
	cin >> n >> q;
	for (int i = 0; i < n; i++) {
		cin >> x[i];
	}
	for (int i = 0; i < q; i++) {
		int a, b;
		cin >> a >> b;
		query[a].push_back(make_pair(b, i));
	}
	for (int i = n; i >= 1; i--) {
		int z = x[i - 1];
		if (fst.count(z)) upd(fst[z], -1);
		fst[z] = i;
		upd(i, 1);
		for (auto t : query[i]) {
			sol[t.second] = qry(t.first);
		}
	}
	for (int i = 0; i < q; i++) {
		cout << sol[i] << '\n';
	}
}