Language: C++

#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int INF = 1e9;
const ll LINF = 1e18;
inline ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
inline ll lcm(ll a, ll b) { return a / gcd(a, b)*b; }
template<class S,class T> ostream& operator << (ostream& out,const pair<S,T>& o){ out << "(" << o.first << "," << o.second << ")"; return out; }
template<class T> ostream& operator << (ostream& out,const vector<T>& V){ for(int i = 0; i < V.size(); i++){ out << V[i]; if(i!=V.size()-1) out << " ";} return out; }
template<class T> ostream& operator << (ostream& out,const vector<vector<T> >& Mat){ for(int i = 0; i < Mat.size(); i++) { if(i != 0) out << endl; out << Mat[i];} return out; }
template<class S,class T> ostream& operator << (ostream& out,const map<S,T>& mp){ out << "{ "; for(auto it = mp.begin(); it != mp.end(); it++){ out << it->first << ":" << it->second; if(mp.size()-1 != distance(mp.begin(),it)) out << ", "; } out << " }"; return out; }
template<typename T>vector<T> make_v(size_t a){return vector<T>(a);}
template<typename T,typename... Ts>auto make_v(size_t a,Ts... ts){return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type fill_v(T &t,const V &v){t=v;}
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type fill_v(T &t,const V &v){for(auto &e:t) fill_v(e,v);}
/*
 <url:>
 問題文============================================================
 =================================================================
 解説=============================================================
 ================================================================
 */

struct Mo {
    using add_func = function<void(int)>;
    using del_func = function<void(int)>;
    using rem_func = function<void(int)>;
    
    int BlockSZ;
    vector<int> L, R, order;
    Mo(int N, int Q, int BlockSZ = -1) : BlockSZ((int)sqrt(N)), order(Q){
        if(BlockSZ != -1) this->BlockSZ = BlockSZ;
        iota(order.begin(), order.end(), 0);
    }
    
    // [l,r)  : 0-index
    void add(int l, int r) {
        L.emplace_back(l);
        R.emplace_back(r);
    }
    
    void run(const add_func &add, const del_func &del, const rem_func &rem) {
        // assert(left.size() == order.size());
        sort(order.begin(), order.end(), [&](int l, int r) {
            int lblock = L[l] / BlockSZ, rblock = L[r] / BlockSZ;
            if(lblock != rblock) return l < r;
            return (lblock&1) ? R[l] < R[r] : R[l] > R[r];
        });
        int nl = 0, nr = 0;
        for(auto idx : order) {
            while(nl > L[idx]){
                nl--;
                add(nl);
            }
            while(nr < R[idx]){
                add(nr);
                nr++;
            }
            while(nl < L[idx]){
                del(nl);
                nl++;
            }
            while(nr > R[idx]){
                nr--;
                del(nr);
            }
            rem(idx);
        }
    }
};


template<class Type>
Type solve(Type res = Type()){
    int N,Q; cin >> N >> Q;
    vector<int> c(N); for(auto& in:c) cin >> in;
    Mo mo(N,Q,700);
    for(int i = 0; i < Q;i++){
        int l,r; cin >> l >> r;
        l--;
        mo.add(l,r);
    }
    
    vector<int> ans(Q);
    vector<int> cnt(N+1);
    int sum = 0;
    auto add = [&](int& id){
        if(cnt[c[id]] == 0) sum++;
        cnt[c[id]]++;
    };
    auto del = [&](int& id){
        cnt[c[id]]--;
        if(cnt[c[id]] == 0) sum--;
    };
    auto rem = [&](int& id){
        ans[id] = sum;
    };
    
    mo.run(add,del,rem);
    for(int i = 0; i < Q;i++){
        cout << ans[i] << "\n";
    }
    
    return res;
}
int main(void) {
    cin.tie(0); ios_base::sync_with_stdio(false);
    solve(0);
    // cout << fixed << setprecision(15) << solve<ll>() << endl;
    return 0;
}


Compiler output:
a.cc: In instantiation of 'Type solve(Type) [with Type = int]':
a.cc:110:10:   required from here
  110 |     solve(0);
      |     ~~~~~^~~
a.cc:101:12: error: cannot convert 'solve<int>(int)::<lambda(int&)>' to 'const Mo::add_func&' {aka 'const std::function<void(int)>&'}
  101 |     mo.run(add,del,rem);
      |            ^~~
      |            |
      |            solve<int>(int)::<lambda(int&)>
a.cc:44:30: note:   initializing argument 1 of 'void Mo::run(const add_func&, const del_func&, const rem_func&)'
   44 |     void run(const add_func &add, const del_func &del, const rem_func &rem) {
      |              ~~~~~~~~~~~~~~~~^~~