Language: C++

#include<iostream>
#include<cstdio>
#include<string>
#include<algorithm>
#include<utility>
#include<numeric>
#include<vector>
#include<map>
#include<set>
#include<tuple>
#include<stack>
#include<queue>
#include<functional>
#include<iterator>
#include<cmath>
#include<cctype>

using namespace std;

typedef pair<int,int> P;
typedef long long ll;

const int INF = 1e9;


int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	int n;
	cin >> n;
	
	int a[n];
	for(int i=0;i<n;i++){
		cin >> a[i];
	}
	sort(a,a+n);

	int prev = -1,ans = 1;
	for(int i=0;i<n;i++){
		if(a[i] == prev) continue;
		ans = max(ans,upper_bound(a,a+n,a[i]+1)-lower_bound(a,a+n,a[i]-1));
		prev = a[i];
	}
	cout << ans << "\n";
				
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:42:26: error: no matching function for call to 'max(int&, long int)'
   42 |                 ans = max(ans,upper_bound(a,a+n,a[i]+1)-lower_bound(a,a+n,a[i]-1));
      |                       ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:42:26: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long int')
   42 |                 ans = max(ans,upper_bound(a,a+n,a[i]+1)-lower_bound(a,a+n,a[i]-1));
      |                       ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/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:42:26: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   42 |                 ans = max(ans,upper_bound(a,a+n,a[i]+1)-lower_bound(a,a+n,a[i]-1));
      |                       ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~