Language: C++

#include <iostream>
#include <vector>
#include <algorithm>
#include <unordered_set>
#include <unordered_map>
#include <utility>
#include <string>

using namespace std;

template<class T>
class RollingHash {
    const int base1 = 1007, base2 = 2009;
    const int mod1 = 1000000007, mod2 = 1000000009;

    vector<long> hash1, hash2, exp1, exp2;

public:
    RollingHash(vector<T> &sequence) :
            hash1(sequence.size() + 1, 0), hash2(sequence.size() + 1, 0),
            exp1(sequence.size() + 1, 1), exp2(sequence.size() + 1, 1) {
        for (int i = 0; i < sequence.size(); ++i) {
            hash1[i + 1] = (hash1[i] * base1 + sequence[i]) % mod1;
            hash2[i + 1] = (hash2[i] * base2 + sequence[i]) % mod2;
            exp1[i + 1] = (exp1[i] * base1) % mod1;
            exp2[i + 1] = (exp2[i] * base2) % mod2;
        }
    }

    pair<long, long> get_hash(int l, int r) const {
        long res1 = hash1[r] - hash1[l] * exp1[r - l] % mod1;
        if (res1 < 0) {
            res1 += mod1;
        }
        long res2 = hash2[r] - hash2[l] * exp2[r - l] % mod2;
        if (res2 < 0) {
            res2 += mod2;
        }
        return {res1, res2};
    }
};


int main() {
    int n;
    string s;
    cin >> n >> s;
    vector<char> seq(s.begin(), s.end());
    RollingHash rh(seq);
    for (int length = seq.size() / 2; length > 0; --length) {
        unordered_map<pair<long, long>, int> cnt;
        for (int i = 0; i <= seq.size() - length; ++i) {
            auto h = rh.get_hash(i, i+length);
            auto item = cnt.find(h);
            if (item != cnt.end() && (item->second + length) <= i) {
                cout << length << endl;
                return 0;
            }
            cnt[h] = i;
        }
    }
    cout << 0 << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:51:46: error: use of deleted function 'std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::unordered_map() [with _Key = std::pair<long int, long int>; _Tp = int; _Hash = std::hash<std::pair<long int, long int> >; _Pred = std::equal_to<std::pair<long int, long int> >; _Alloc = std::allocator<std::pair<const std::pair<long int, long int>, int> >]'
   51 |         unordered_map<pair<long, long>, int> cnt;
      |                                              ^~~
In file included from /usr/include/c++/14/unordered_map:41,
                 from a.cc:5:
/usr/include/c++/14/bits/unordered_map.h:148:7: note: 'std::unordered_map<_Key, _Tp, _Hash, _Pred, _Alloc>::unordered_map() [with _Key = std::pair<long int, long int>; _Tp = int; _Hash = std::hash<std::pair<long int, long int> >; _Pred = std::equal_to<std::pair<long int, long int> >; _Alloc = std::allocator<std::pair<const std::pair<long int, long int>, int> >]' is implicitly deleted because the default definition would be ill-formed:
  148 |       unordered_map() = default;
      |       ^~~~~~~~~~~~~
/usr/include/c++/14/bits/unordered_map.h: At global scope:
/usr/include/c++/14/bits/unordered_map.h:148:7: error: use of deleted function 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _Alloc = std::allocator<std::pair<const std::pair<long int, long int>, int> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long int, long int> >; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>]'
In file included from /usr/include/c++/14/bits/unordered_set.h:33,
                 from /usr/include/c++/14/unordered_set:41,
                 from a.cc:4:
/usr/include/c++/14/bits/hashtable.h:539:7: note: 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _Alloc = std::allocator<std::pair<const std::pair<long int, long int>, int> >; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long int, long int> >; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _RehashPolicy = std::__detail::_Prime_rehash_policy; _Traits = std::__detail::_Hashtable_traits<true, false, true>]' is implicitly deleted because the default definition would be ill-formed:
  539 |       _Hashtable() = default;
      |       ^~~~~~~~~~
/usr/include/c++/14/bits/hashtable.h:539:7: error: use of deleted function 'std::__detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _Traits>::_Hashtable_base() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long int, long int> >; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, false, true>]'
In file included from /usr/include/c++/14/bits/hashtable.h:35:
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: note: 'std::__detail::_Hashtable_base<_Key, _Value, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _Traits>::_Hashtable_base() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _ExtractKey = std::__detail::_Select1st; _Equal = std::equal_to<std::pair<long int, long int> >; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, false, true>]' is implicitly deleted because the default definition would be ill-formed:
 1731 |       _Hashtable_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: error: use of deleted function 'std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __cache_hash_code>::_Hash_code_base() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _ExtractKey = std::__detail::_Select1st; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; bool __cache_hash_code = true]'
/usr/include/c++/14/bits/hashtable_policy.h: In instantiation of 'std::__detail::_Hashtable_ebo_helper<_Nm, _Tp, true>::_Hashtable_ebo_helper() [with int _Nm = 1; _Tp = std::hash<std::pair<long int, long int> >]':
/usr/include/c++/14/bits/hashtable_policy.h:1328:7:   required from here
 1328 |       _Hash_code_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1245:49: error: use of deleted function 'std::hash<std::pair<long int, long int> >::hash()'
 1245 |       _Hashtable_ebo_helper() noexcept(noexcept(_Tp())) : _Tp() { }
      |                                                 ^~~~~
In file included from /usr/include/c++/14/string_view:50,
                 from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<long int, long int> >::hash()' is implicitly deleted because the default definition would be ill-formed:
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:102:12: error: no matching function for call to 'std::__hash_enum<std::pair<long int, long int>, false>::__hash_enum()'
/usr/include/c++/14/bits/functional_hash.h:83:7: note: candidate: 'std::__hash_enum<_Tp, <anonymous> >::__hash_enum(std::__hash_enum<_Tp, <anonymous> >&&) [with _Tp = std::pair<long int, long int>; bool <anonymous> = false]'
   83 |       __hash_enum(__hash_enum&&);
      |       ^~~~~~~~~~~
/usr/include/c++/14/bits/functional_hash.h:83:7: note:   candidate expects 1 argument, 0 provided
/usr/include/c++/14/bits/functional_hash.h:102:12: error: 'std::__hash_enum<_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<long int, long int>; bool <anonymous> = false]' is private within this context
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:84:7: note: declared private here
   84 |       ~__hash_enum();
      |       ^
/usr/include/c++/14/bits/hashtable_policy.h:1245:49: note: use '-fdiagnostics-all-candidates' to display considered candidates
 1245 |       _Hashtable_ebo_helper() noexcept(noexcept(_Tp())) : _Tp() { }
      |                                                 ^~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1328:7: note: 'std::__detail::_Hash_code_base<_Key, _Value, _ExtractKey, _Hash, _RangeHash, _Unused, __cache_hash_code>::_Hash_code_base() [with _Key = std::pair<long int, long int>; _Value = std::pair<const std::pair<long int, long int>, int>; _ExtractKey = std::__detail::_Select1st; _Hash = std::hash<std::pair<long int, long int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; bool __cache_hash_code = true]' is implicitly deleted because the default definition would be ill-formed:
 1328 |       _Hash_code_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1328:7: error: use of deleted function 'std::__detail::_Hashtable_ebo_helper<1, std::hash<std::pair<long int, long int> >, true>::~_Hashtable_ebo_helper()'
/usr/include/c++/14/bits/hashtable_policy.h:1242:12: note: 'std::__detail::_Hashtable_ebo_helper<1, std::hash<std::pair<long int, long int> >, true>::~_Hashtable_ebo_helper()' is implicitly deleted because the default definition would be ill-formed:
 1242 |     struct _Hashtable_ebo_helper<_Nm, _Tp, true>
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1242:12: error: use of deleted function 'std::hash<std::pair<long int, long int> >::~hash()'
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<long int, long int> >::~hash()' is implicitly deleted because the default definition would be ill-formed:
  102 |     struct hash : __hash_enum<_Tp>
      |            ^~~~
/usr/include/c++/14/bits/functional_hash.h:102:12: error: 'std::__hash_enum<_Tp, <anonymous> >::~__hash_enum() [with _Tp = std::pair<long int, long int>; bool <anonymous> = false]' is private within this context
/usr/include/c++/14/bits/functional_hash.h:84:7: note: declared private here
   84 |       ~__hash_enum();
      |       ^
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: note: use '-fdiagnostics-all-candidates' to display considered candidates
 1731 |       _Hashtable_base() = default;
      |       ^~~~~~~~~~~~~~~
/usr/include/c++/14/bits/hashtable_policy.h:1731:7: error: use of deleted function 'std::__detail::_Hash_code_base<std::pair<long int, long int>, std::pair<const std::pair<long int, long int>, int>, std::__detail::_Select1st, std::hash<std::pair<long int, long int> >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, true>::~_Hash_code_base()'
/usr/include/c++/14/bits/hashtable_policy.h:1306:12: note: 'std::__detail::_Hash_code_base<std::pair<long int, long int>, std::pair<const std::pair<long int, long int>, int>, std::__detail::_Select1st, std::hash<std::pair<long int, long int> >, std::__detail::