Language: C++

#include <bits/stdc++.h>

using namespace std;
#define ll long long
const int N=2e5+5;
ll INF=1e18;
ll a[N];
int n;
ll k;
ll UP(ll r,ll a)
{
    bool f1=0,f2=0;
    if(r%a!=0) f1=1;
    if(r>=0&&a>=0||r<0&&a<0) f2=1;
    r/=a;
    r+=(f1&&f2);
    return r;
}
ll LOW(ll r,ll a)
{
    bool f1=0,f2=1;
    if(r%a!=0) f1=1;
    if(r>=0&&a>=0||r<0&&a<0) f2=0;
    r/=a;
    r-=(f1&&f2);
    return r;
}
bool valid(ll r)
{
    ll cnt=0;
    for(int i=0;i<n;i++)
    {
        if(a[i]>0)
        {
            int idx=upper_bound(a,a+n,LOW(r,a[i]))-a-1;
            cnt+=max(0,idx-i);
        }
        else if(a[i]<0) cnt+=n-max(i+1,lower_bound(a,a+n,UP(r,a[i]))-a);
        else if(0<=r) cnt+=n-(i+1);
    }
    return cnt>=k;
}
ll solve()
{
    ll s=-INF,e=INF,mid;
    while(s<e)
    {
        mid=s+(e-s)/2;
        if(valid(mid)) e=mid;
        else s=mid+1;
    }
    return s;
}
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    cin>>n>>k;
    for(int i=0;i<n;i++)
        cin>>a[i];
    sort(a,a+n);
    cout<<solve()<<endl;
    return 0;
}


Compiler output:
a.cc: In function 'bool valid(long long int)':
a.cc:38:35: error: no matching function for call to 'max(int, long int)'
   38 |         else if(a[i]<0) cnt+=n-max(i+1,lower_bound(a,a+n,UP(r,a[i]))-a);
      |                                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 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:38:35: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long int')
   38 |         else if(a[i]<0) cnt+=n-max(i+1,lower_bound(a,a+n,UP(r,a[i]))-a);
      |                                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/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:
/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:38:35: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   38 |         else if(a[i]<0) cnt+=n-max(i+1,lower_bound(a,a+n,UP(r,a[i]))-a);
      |                                ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~