Language: C++

#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <map>
#define rep(i, n) for(int i = 0; i < n; i++)
using namespace std;
typedef long long ll;
const ll mod = 1000000007;

vector<ll> C(60, vector<ll>(60));

void PascalTriangle() {

    rep(i, 60) {
        C[i][0] = C[i][i] = 1;
    }

    for(int i = 2; i < 60; i++) {
        for(int j = 1; j < i; j++) {
            C[i][j] = C[i-1][j] + C[i-1][j-1];
        }
    }
}

int main() {
    int n, a, b;
    cin >> n >> a >> b;

    vector<ll> v(n);
    rep(i, n) {
        cin >> v[i];
    } 
    sort(v.begin(), v.end());
    reverse(v.begin(), v.end());

    ll sum = 0;
    rep(i, a) {
        sum += v[i];
    }
    double avg = (double)sum/a;
    printf("%.7f\n", avg);

    PascalTriangle();

    ll ans = 0;
    if(v[0] != v[a-1]) {

        int x = 0, y = 0;
        rep(i, n) {
            if(v[i] == v[a-1]) {
                x++;
            }
        }
        rep(i, a) {
            if(v[i] == v[a-1]) {
                y++;
            }
        }

        ans = C[x][y];
    }
    else if(v[0] == v[a-1]) {

        int x = 0;
        rep(i, n) {
            if(v[i] == v[0]) {
                x++;
            }
        }

        for(int i = a; i <= min(b, x); i++) {
            ans += C[x][i];
        }
    }

    cout << ans << endl;
    return 0;
}

Compiler output:
a.cc:16:32: error: no matching function for call to 'std::vector<long long int>::vector(int, std::vector<long long int>)'
   16 | vector<ll> C(60, vector<ll>(60));
      |                                ^
In file included from /usr/include/c++/14/vector:66,
                 from a.cc:7:
/usr/include/c++/14/bits/stl_vector.h:707:9: note: candidate: 'template<class _InputIterator, class> std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) [with <template-parameter-2-2> = _InputIterator; _Tp = long long int; _Alloc = std::allocator<long long int>]'
  707 |         vector(_InputIterator __first, _InputIterator __last,
      |         ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:707:9: note:   template argument deduction/substitution failed:
a.cc:16:32: note:   deduced conflicting types for parameter '_InputIterator' ('int' and 'std::vector<long long int>')
   16 | vector<ll> C(60, vector<ll>(60));
      |                                ^
/usr/include/c++/14/bits/stl_vector.h:678:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::initializer_list<_Tp>, const allocator_type&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; allocator_type = std::allocator<long long int>]'
  678 |       vector(initializer_list<value_type> __l,
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:678:43: note:   no known conversion for argument 1 from 'int' to 'std::initializer_list<long long int>'
  678 |       vector(initializer_list<value_type> __l,
      |              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:659:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, std::__type_identity_t<_Alloc>&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; std::__type_identity_t<_Alloc> = std::allocator<long long int>]'
  659 |       vector(vector&& __rv, const __type_identity_t<allocator_type>& __m)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:659:23: note:   no known conversion for argument 1 from 'int' to 'std::vector<long long int>&&'
  659 |       vector(vector&& __rv, const __type_identity_t<allocator_type>& __m)
      |              ~~~~~~~~~^~~~
/usr/include/c++/14/bits/stl_vector.h:640:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, const allocator_type&, std::false_type) [with _Tp = long long int; _Alloc = std::allocator<long long int>; allocator_type = std::allocator<long long int>; std::false_type = std::false_type]'
  640 |       vector(vector&& __rv, const allocator_type& __m, false_type)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:640:7: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_vector.h:635:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&, const allocator_type&, std::true_type) [with _Tp = long long int; _Alloc = std::allocator<long long int>; allocator_type = std::allocator<long long int>; std::true_type = std::true_type]'
  635 |       vector(vector&& __rv, const allocator_type& __m, true_type) noexcept
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:635:7: note:   candidate expects 3 arguments, 2 provided
/usr/include/c++/14/bits/stl_vector.h:624:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&, std::__type_identity_t<_Alloc>&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; std::__type_identity_t<_Alloc> = std::allocator<long long int>]'
  624 |       vector(const vector& __x, const __type_identity_t<allocator_type>& __a)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:624:28: note:   no known conversion for argument 1 from 'int' to 'const std::vector<long long int>&'
  624 |       vector(const vector& __x, const __type_identity_t<allocator_type>& __a)
      |              ~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:620:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(std::vector<_Tp, _Alloc>&&) [with _Tp = long long int; _Alloc = std::allocator<long long int>]'
  620 |       vector(vector&&) noexcept = default;
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:620:7: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_vector.h:601:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const std::vector<_Tp, _Alloc>&) [with _Tp = long long int; _Alloc = std::allocator<long long int>]'
  601 |       vector(const vector& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:601:7: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_vector.h:569:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(size_type, const value_type&, const allocator_type&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; size_type = long unsigned int; value_type = long long int; allocator_type = std::allocator<long long int>]'
  569 |       vector(size_type __n, const value_type& __value,
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:569:47: note:   no known conversion for argument 2 from 'std::vector<long long int>' to 'const std::vector<long long int>::value_type&' {aka 'const long long int&'}
  569 |       vector(size_type __n, const value_type& __value,
      |                             ~~~~~~~~~~~~~~~~~~^~~~~~~
/usr/include/c++/14/bits/stl_vector.h:556:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(size_type, const allocator_type&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; size_type = long unsigned int; allocator_type = std::allocator<long long int>]'
  556 |       vector(size_type __n, const allocator_type& __a = allocator_type())
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:556:51: note:   no known conversion for argument 2 from 'std::vector<long long int>' to 'const std::vector<long long int>::allocator_type&' {aka 'const std::allocator<long long int>&'}
  556 |       vector(size_type __n, const allocator_type& __a = allocator_type())
      |                             ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:542:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector(const allocator_type&) [with _Tp = long long int; _Alloc = std::allocator<long long int>; allocator_type = std::allocator<long long int>]'
  542 |       vector(const allocator_type& __a) _GLIBCXX_NOEXCEPT
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:542:7: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_vector.h:531:7: note: candidate: 'std::vector<_Tp, _Alloc>::vector() [with _Tp = long long int; _Alloc = std::allocator<long long int>]'
  531 |       vector() = default;
      |       ^~~~~~
/usr/include/c++/14/bits/stl_vector.h:531:7: note:   candidate expects 0 arguments, 2 provided
a.cc: In function 'void PascalTriangle()':
a.cc:21:13: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   21 |         C[i][0] = C[i][i] = 1;
      |             ^
a.cc:21:23: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   21 |         C[i][0] = C[i][i] = 1;
      |                       ^
a.cc:26:17: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   26 |             C[i][j] = C[i-1][j] + C[i-1][j-1];
      |                 ^
a.cc:26:29: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   26 |             C[i][j] = C[i-1][j] + C[i-1][j-1];
      |                             ^
a.cc:26:41: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   26 |             C[i][j] = C[i-1][j] + C[i-1][j-1];
      |                                         ^
a.cc: In function 'int main()':
a.cc:66:19: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   66 |         ans = C[x][y];
      |                   ^
a.cc:78:24: error: invalid types '__gnu_cxx::__alloc_traits<std::allocator<long long int>, long long int>::value_type {aka long long int}[int]' for array subscript
   78 |             ans += C[x][i];
      |                        ^