Sum of ones

#include <bits/stdc++.h>

#define REP(i, a, b) for (int i = a; i < b; i++)

// Type Aliases for 1D and 2D vectors with initialization
#define vll(n, val) vector<long long>(n, val) // 1D vector of long longs with size n, initialized to val
#define ll long long
#define vvi(n, m, val) vector<vector<int>>(n, vector<int>(m, val))              // 2D vector of ints (n x m), initialized to val
#define vvll(n, m, val) vector<vector<long long>>(n, vector<long long>(m, val)) // 2D vector of long longs (n x m), initialized to val

using namespace std;

void print_vector(vector<int> &x)
{
    for (int v : x)
    {
        cout << v << " ";
    }
    cout << "\n";
}

void print_matrix(vector<vector<int>> &matrix)
{
    cout << "\n"
         << "----------------" << "\n";
    for (vector<int> row : matrix)
    {
        print_vector(row);
    }
    cout << "\n"
         << "----------------" << "\n";
}

int one_count(int n)
{
    int result = 0;
    while (n > 0)
    {
        result += n % 2;
        n /= 2;
    }
    return result;
}

long long highest_set_bit(ll n)
{
    long long exponent = 0;
    while (n > 1)
    {
        exponent++;
        n /= 2;
    }
    return exponent;
}

ll sum_ones(ll n)
{
    if (n == 0)
    {
        return 0;
    }
    long long no_bits = highest_set_bit(n);
    ll lp2 = (ll)1 << no_bits; // next lowest power of 2

    ll ones_until_lp2 = no_bits * ((ll)1 << (no_bits - 1));
    ll r = n - lp2;
    ll ones_from_highest_bit = r + 1;
    return ones_until_lp2 + ones_from_highest_bit + sum_ones(r);
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll n;
    cin >> n;

    cout << sum_ones(n) << "\n";
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED