Language: C++

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define pb push_back
#define INF 0x3f3f3f3
#define LINF 0x3f3f3f3f3f3f3f
#define MAXN int(1e5)+5
#define fim '\n'
#define ll long long
#define f first
#define s second
#define FAST cin.tie(0), cout.tie(0), ios::sync_with_stdio(0)
#define debug(x) cout << "DEBUG " << x << fim
#define debug2(x, y) cout << "DEBUG " << x << " " << y << fim
#define debug3(x, y, z) cout << "DEBUG " << x << " " << y << " " << z<< fim
#define debug4(x, y, z, o) cout << "DEBUG " << x << " " << y << " " << z<< " " << o << fim
#define max3(x, y, z) max(x, max(y, z))
#define ull unsigned long long
using namespace std;
using namespace __gnu_pbds;
typedef pair<int, int> pii;
typedef pair<string, int> psi;
typedef pair<unsigned ll, pair<int, int> > piii;
typedef pair<pair<int, int>, int> piii2;
typedef tree<int,null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> indexed_set;
const ll MOD = 1e9+7;

ll dist[MAXN], mec = 0, start = 0, n, v[n+5];
bool used[MAXN];

void bfs(start) {
    
    mec = v[start];
    
    for(int i = 0; i < n; i++)
        dist[i] = -LINF;
    
    priority_queue<piii> fila;
    fila.pb({v[start], 0}, start});
    dist[start] = v[start];
    
    while(!fila.empty()) {
        int u = fila.top().f.f;
        int qtd = fila.top().f.s;
        fila.pop();
        
        if(fila.top().f.s == n/2)
            continue;
        for(auto i : g[u])
            if(dist[i] < dist[u]+v[i]) {
                dist[i] = dist[u]+v[i];
                fila.push({{dist[i], qtd+1}, i});
            }
            
    }
    
    for(int i = 0; i < n; i++) 
        if(dist[i] > mec) {
            start = i;
            mec = dist[i];
        }
    
}

int main() {

    cin >> n;
    

    for(int i = 0; i < n; i++) {
        cin >> v[i];
    	if(v[i] > v[start])
          	start = i;
    }

    unordered_set<pii> edges;
    
    for(int i = 0; i < n; i++) {
        if(i < n-2)
            g[i].pb(i+2);
        if(i >= 2)
            g[i].pb(i-2);
    }
    
    bfs(start);
    bfs(start);
    cout << mec << endl;
    
}

Compiler output:
a.cc:27:42: error: size of array 'v' is not an integral constant-expression
   27 | ll dist[MAXN], mec = 0, start = 0, n, v[n+5];
      |                                         ~^~
a.cc:30:6: error: variable or field 'bfs' declared void
   30 | void bfs(start) {
      |      ^~~
a.cc:38:34: error: expected unqualified-id before ')' token
   38 |     fila.pb({v[start], 0}, start});
      |                                  ^
a.cc:39:5: error: 'dist' does not name a type
   39 |     dist[start] = v[start];
      |     ^~~~
a.cc:41:5: error: expected unqualified-id before 'while'
   41 |     while(!fila.empty()) {
      |     ^~~~~
a.cc:56:5: error: expected unqualified-id before 'for'
   56 |     for(int i = 0; i < n; i++)
      |     ^~~
a.cc:56:20: error: 'i' does not name a type
   56 |     for(int i = 0; i < n; i++)
      |                    ^
a.cc:56:27: error: 'i' does not name a type
   56 |     for(int i = 0; i < n; i++)
      |                           ^
a.cc:62:1: error: expected declaration before '}' token
   62 | }
      | ^
a.cc: In function 'int main()':
a.cc:75:24: error: use of deleted function 'std::unordered_set<_Value, _Hash, _Pred, _Alloc>::unordered_set() [with _Value = std::pair<int, int>; _Hash = std::hash<std::pair<int, int> >; _Pred = std::equal_to<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]'
   75 |     unordered_set<pii> edges;
      |                        ^~~~~
In file included from /usr/include/c++/14/unordered_set:41,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:189,
                 from a.cc:1:
/usr/include/c++/14/bits/unordered_set.h:142:7: note: 'std::unordered_set<_Value, _Hash, _Pred, _Alloc>::unordered_set() [with _Value = std::pair<int, int>; _Hash = std::hash<std::pair<int, int> >; _Pred = std::equal_to<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]' is implicitly deleted because the default definition would be ill-formed:
  142 |       unordered_set() = default;
      |       ^~~~~~~~~~~~~
/usr/include/c++/14/bits/unordered_set.h: At global scope:
/usr/include/c++/14/bits/unordered_set.h:142:7: error: use of deleted function 'std::_Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal, _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::_Hashtable() [with _Key = std::pair<int, int>; _Value = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >; _ExtractKey = std::__detail::_Identity; _Equal = std::equal_to<std::pair<int, int> >; _Hash = std::hash<std::pair<int, 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, true, true>]'
In file included from /usr/include/c++/14/bits/unordered_map.h:33,
                 from /usr/include/c++/14/unordered_map:41,
                 from /usr/include/c++/14/functional:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53:
/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<int, int>; _Value = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >; _ExtractKey = std::__detail::_Identity; _Equal = std::equal_to<std::pair<int, int> >; _Hash = std::hash<std::pair<int, 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, true, 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<int, int>; _Value = std::pair<int, int>; _ExtractKey = std::__detail::_Identity; _Equal = std::equal_to<std::pair<int, int> >; _Hash = std::hash<std::pair<int, int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, true, 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<int, int>; _Value = std::pair<int, int>; _ExtractKey = std::__detail::_Identity; _Equal = std::equal_to<std::pair<int, int> >; _Hash = std::hash<std::pair<int, int> >; _RangeHash = std::__detail::_Mod_range_hashing; _Unused = std::__detail::_Default_ranged_hash; _Traits = std::__detail::_Hashtable_traits<true, true, 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<int, int>; _Value = std::pair<int, int>; _ExtractKey = std::__detail::_Identity; _Hash = std::hash<std::pair<int, 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<int, 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<int, 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/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<int, 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<int, 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<int, 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<int, 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<int, int>; _Value = std::pair<int, int>; _ExtractKey = std::__detail::_Identity; _Hash = std::hash<std::pair<int, 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<int, 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<int, 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<int, int> >::~hash()'
/usr/include/c++/14/bits/functional_hash.h:102:12: note: 'std::hash<std::pair<int, 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<int, 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<int, int>, std::pair<int, int>, std::__detail::_Identity, std::hash<std::pair<int, int> >, std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash, true>::~_Hash_cod