Сформировать новый массив на основе исходного, согласно условию

#include <iostream>
#include <vector>
#include <algorithm>
#include <ctime>
#include <random>
 
int main()
{
    const size_t FROM_NUM = 10;
    const size_t TO_NUM = 20;
    
    std::mt19937 mt( time( nullptr ) );
    std::uniform_int_distribution<size_t> dist( FROM_NUM, TO_NUM );
    
    size_t N = dist( mt );
 
    std::vector<size_t> A(N);
    
    for ( auto & elem : A )
        elem = dist( mt );
 
    for ( const auto & elem : A )
        std::cout << elem << " ";
    std::cout << "\n";
 
    std::vector<size_t> B(N);
 
    std::copy( A.begin(), A.end() , B.begin() );
    std::random_shuffle ( B.begin() + 1, B.end() - 1 );
    
    *B.begin() = 99;
    B.back() =  99;
 
    for ( const auto & elem : B )
        std::cout << elem << " ";
    std::cout << "\n";
 
    return 0;
}

#include <algorithm>
#include <iostream>
#include <iterator>
#include <random>
 
int main()
{
    const int N = 15;
    int A[N] = {}, B[N] = {};
    std::mt19937 gen {std::random_device()()};
    std::uniform_int_distribution<> dist(0, 9);
    std::generate(A, A + N, [&dist, &gen] { return dist(gen); });
    const int first = A[0], last = A[N-1];
    std::copy_if(A+1, A + N-1, B, [first, last](const int x) { return x != first && x != last; });
    std::copy(A, A + N, std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;
    std::copy(B, B + N, std::ostream_iterator<int>(std::cout, " "));
}

#include <algorithm>
#include <array>
#include <iostream>
#include <iterator>
#include <random>
 
int main()
{
    std::array<int, 15> A, B={};
    std::mt19937 gen {std::random_device()()};
    std::uniform_int_distribution<> dist(0, 9);
    std::generate(A.begin(), A.end(), [&dist, &gen] { return dist(gen); });
    std::copy_if(A.begin()+1, A.end()-1, B.begin(), [&A](const int x) { return x != A.front() && x != A.back(); });
    std::copy(A.begin(), A.end(), std::ostream_iterator<int>(std::cout, " "));
    std::cout << std::endl;
    std::copy(B.begin(), B.end(), std::ostream_iterator<int>(std::cout, " "));
}