Language: C++

#include <bits/stdc++.h>
using namespace std;

void update_dpk12(int k, vector<int> & dp1, vector<int> & dp2, const vector<int> & As){
    int m1, m2;
    if (As[0] > As[k]){
        m1 = As[0];
        m2 = As[k];
        dp1[k] = 0;
        dp2[k] = k;
    }else{
        m1 = As[k];
        m2 = As[0];
        dp1[k] = k;
        dp2[k] = 0;
    }
    for (int mask = 1; mask < k; mask <<= 1) {
        if ((mask & k) == 0) continue;
        int s = k ^mask;
        if (As[dp1[s]] > m1) {
            dp2[k] = dp1[k];
            dp1[k] = dp1[s];
            m2 = m1;
            m1 = As[dp1[s]];
        }else if (As[dp1[s]] == m1){
            if (dp1[s] != dp1[k]){
                dp2[k] = dp1[s];
                m2 = m1;
            }
        }else if (As[dp1[s]] > m2){
            dp2[k] = dp1[s];
            m2 = As[dp1[s]];
        }
        if (s > 0 and As[dp2[s]] > m2 ){
            dp2[k] = dp2[s];
            m2 = As[dp2[s]];
        }
    }
}


int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    const int L = (1 << N);
    vector<int> As(L);
    for (auto & a : As) cin >> a;

    vector<int> dp1(L);
    vector<int> dp2(L);
    // dp1[k]  k の bit列 のサブセット i について、Aiが最大となるときの i
    // dp2[k]　k の bit列 のサブセット i について、Aiが２番目に大きい値となるときの i

    dp1[0] = 0;
    dp2[0] = -1;
    dp1[1] = (As[0] > As[1]) ? 0 : 1;
    dp2[1] = 1 - dp1[1];

    int ans = As[0] + As[1];
    cout << ans << '\n';

    for (int k = 2; k < L; ++k){
        update_dpk12(k, dp1, dp2, As);
        ans = max(ans, As[dp1[k]] + As[dp2]);
        cout << ans << '\n';
    }

    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:66:39: error: no match for 'operator[]' (operand types are 'std::vector<int>' and 'std::vector<int>')
   66 |         ans = max(ans, As[dp1[k]] + As[dp2]);
      |                                       ^
In file included from /usr/include/c++/14/vector:66,
                 from /usr/include/c++/14/functional:64,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:53,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_vector.h:1128:7: note: candidate: 'std::vector<_Tp, _Alloc>::reference std::vector<_Tp, _Alloc>::operator[](size_type) [with _Tp = int; _Alloc = std::allocator<int>; reference = int&; size_type = long unsigned int]'
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1128:28: note:   no known conversion for argument 1 from 'std::vector<int>' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1128 |       operator[](size_type __n) _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_vector.h:1147:7: note: candidate: 'std::vector<_Tp, _Alloc>::const_reference std::vector<_Tp, _Alloc>::operator[](size_type) const [with _Tp = int; _Alloc = std::allocator<int>; const_reference = const int&; size_type = long unsigned int]'
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_vector.h:1147:28: note:   no known conversion for argument 1 from 'std::vector<int>' to 'std::vector<int>::size_type' {aka 'long unsigned int'}
 1147 |       operator[](size_type __n) const _GLIBCXX_NOEXCEPT
      |                  ~~~~~~~~~~^~~