Language: C++

#include<bits/stdc++.h>

using namespace std;

#define int long long
#define ALL(x) (x).begin(),(x).end()
#define MAX(x) *max_element(ALL(x))
#define MIN(x) *min_element(ALL(x))

typedef pair<int,int> PI;
typedef pair<int,pair<int,int>> PII;
static const int INF=1010000000000000017LL;
static const double eps=1e-12;
static const double pi=3.14159265358979323846;
static const int dx[4]={1,-1,0,0};
static const int dy[4]={0,0,1,-1};
static const int ddx[8]={1,-1,0,0,1,1,-1,-1};
static const int ddy[8]={0,0,1,-1,1,-1,1,-1};

template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return true;}return false;}
template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return true;}return false;}

template<typename T>
struct Vector2 {
    T x, y;
    Vector2() {}
    Vector2(T x, T y) : x(x), y(y) {}
    void operator=(const Vector2 &other) {
        x = other.x;
        y = other.y;
    }
    Vector2 operator+(const Vector2 &other) {
        return Vector2I(x + other.x, y + other.y);
    }
    Vector2 operator-(const Vector2 &other) {
        return Vector2I(x - other.x, y - other.y);
    }
    bool operator==(const Vector2 &other) {
        return (x == other.x && y == other.y);
    }
    int dot(Vector2 other) {
        return x * other.x + y * other.y;
    }
    int det(Vector2 other) {
        return x * other.y - y * other.x;
    }
};

template<typename T>
bool cmp_x(const Vector2<T> &p, const Vector2<T> &q) {
    if(p.x != q.x) return p.x < q.x;
    return p.y < q.y;
}

template<typename T>
vector<T> convexhull(vector<Vector2<T>> &ps) {
    sort(ps.begin() , ps.end(), cmp_x<T>);
    int size = ps.size();
    int k = 0;
    if (size <= 2) return ps;
    vector<Vector2<T>> qs(size * 2);
    for (int i = 0; i < size; ++i) {
        while (k > 1 && (qs[k - 2] - qs[k - 1]).det(ps[i] - qs[k - 1]) <= 0) k--;
        qs[k++] = ps[i];
    }
    for (int i = size - 2, t = k; i >= 0; i--) {
        while(k > t && (qs[k - 2] - qs[k - 1]).det(ps[i] - qs[k - 1]) <= 0) k--;
        qs[k++] = ps[i];
    }
    qs.resize(k - 1);
    return qs;
}

int N;
vector<Vector2<int>> P;

signed main(){
    cin>>N;
    for(int i=0;i<N;++i){
        int x,y;
        cin>>x>>y;
        P.push_back(Vector2(x,y));
    }
    auto qs=convexhull(P);
    int ans=0;
    for(int i=0;i<qs.size()-1;++i){
        for(int j=i+1;j<qs.size();++j){
            int d=abs(qs[i].x-qs[j].x)+abs(qs[i].y-qs[j].y);
            chmax(ans,d);
        }
    }
    cout<<ans<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:88:29: error: request for member 'x' in 'qs.std::vector<long long int, std::allocator<long long int> >::operator[](((std::vector<long long int, std::allocator<long long int> >::size_type)i))', which is of non-class type '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type' {aka 'long long int'}
   88 |             int d=abs(qs[i].x-qs[j].x)+abs(qs[i].y-qs[j].y);
      |                             ^
a.cc:88:37: error: request for member 'x' in 'qs.std::vector<long long int, std::allocator<long long int> >::operator[](((std::vector<long long int, std::allocator<long long int> >::size_type)j))', which is of non-class type '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type' {aka 'long long int'}
   88 |             int d=abs(qs[i].x-qs[j].x)+abs(qs[i].y-qs[j].y);
      |                                     ^
a.cc:88:50: error: request for member 'y' in 'qs.std::vector<long long int, std::allocator<long long int> >::operator[](((std::vector<long long int, std::allocator<long long int> >::size_type)i))', which is of non-class type '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type' {aka 'long long int'}
   88 |             int d=abs(qs[i].x-qs[j].x)+abs(qs[i].y-qs[j].y);
      |                                                  ^
a.cc:88:58: error: request for member 'y' in 'qs.std::vector<long long int, std::allocator<long long int> >::operator[](((std::vector<long long int, std::allocator<long long int> >::size_type)j))', which is of non-class type '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type' {aka 'long long int'}
   88 |             int d=abs(qs[i].x-qs[j].x)+abs(qs[i].y-qs[j].y);
      |                                                          ^
a.cc: In instantiation of 'std::vector<_Tp> convexhull(std::vector<Vector2<T> >&) [with T = long long int]':
a.cc:84:23:   required from here
   84 |     auto qs=convexhull(P);
      |             ~~~~~~~~~~^~~
a.cc:60:27: error: could not convert 'ps' from 'vector<Vector2<long long int>,allocator<Vector2<long long int>>>' to 'vector<long long int,allocator<long long int>>'
   60 |     if (size <= 2) return ps;
      |                           ^~
      |                           |
      |                           vector<Vector2<long long int>,allocator<Vector2<long long int>>>
a.cc:71:12: error: could not convert 'qs' from 'vector<Vector2<long long int>,allocator<Vector2<long long int>>>' to 'vector<long long int,allocator<long long int>>'
   71 |     return qs;
      |            ^~
      |            |
      |            vector<Vector2<long long int>,allocator<Vector2<long long int>>>