Language: C++

#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <string>
#include <map>
#include <stdio.h>
#include <stdlib.h>
using namespace std;

static const double pi = 3.14159265358979323846;

int main(){
  int N;
  cin >> N;

  map<int,int> honsuu;
  map<int,bool> nihonijou;
  map<int,bool> yonhonijou;
  for(int i=0; i<N; i++){
    int A;
    cin >> A;
    if(honsuu.find(A) != honsuu.end()){
      ++honsuu[A];
      if(honsuu[A]==2) nihonijou[A] = true;
      if(honsuu[A]==4) yonhonijou[A] = true;
    }
    else{
      honsuu[A] = 1;
    }
  }

  long long max_area = 0;
  if(nihonijou.size() > 1){
    auto itr = nihonijou.end();
    int a = (--itr)->first;
    int b = (--itr)->first;
    max_area = max(a*b,max_area);
  }
  if(yonhonijou.size() > 0){
    auto itr = yonhonijou.end();
    int a = (--itr)->first;
    max_area = max(a*a,max_area);
  }

    cout << max_area << endl;


  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:38:19: error: no matching function for call to 'max(int, long long int&)'
   38 |     max_area = max(a*b,max_area);
      |                ~~~^~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 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/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:38:19: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long long int')
   38 |     max_area = max(a*b,max_area);
      |                ~~~^~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61,
                 from a.cc:4:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:38:19: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   38 |     max_area = max(a*b,max_area);
      |                ~~~^~~~~~~~~~~~~~
a.cc:43:19: error: no matching function for call to 'max(int, long long int&)'
   43 |     max_area = max(a*a,max_area);
      |                ~~~^~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:43:19: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long long int')
   43 |     max_area = max(a*a,max_area);
      |                ~~~^~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:43:19: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   43 |     max_area = max(a*a,max_area);
      |                ~~~^~~~~~~~~~~~~~