Problem p02609 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, n) for (int i = 1; i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define debug(var)                                                             \
  do {                                                                         \
    cout << #var << " : ";                                                     \
    view(var);                                                                 \
  } while (0)
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
using namespace std;
template <class T> void view(T e) { cout << e << endl; }
template <class T> void view(const vector<T> &v) {
  for (const auto &e : v) {
    cout << e << " ";
  }
  cout << endl;
}
template <class T> void view(const vector<vector<T>> &vv) {
  for (const auto &v : vv) {
    view(v);
  }
}
using vint = vector<int>;
using vvint = vector<vector<int>>;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<int, int>;
const int inf = 1e9;
const ll inf_l = 1e18;
const int MAX = 1e5;

long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

int f(string s, int div) {
  int n = s.size();
  ll x = 0;
  rep(i, n) {
    if (s[i] == '1') {
      x += modpow(2, n - 1 - i, div);
      x %= div;
    }
  }
  return x % div;
}

int f_(int x, int ct = 1) {
  if (x == 0)
    return ct;
  int tmp = x % __builtin_popcount(x);
  if (tmp == 0)
    return ct + 1;
  return f_(tmp, ct + 1);
}

int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  int div = 0;
  rep(i, n) if (s[i] == '1') div++;
  int x_plus = f(s, div + 1);
  int x_minus = f(s, div - 1);
  rep(i, n) {
    int div_tmp = div;
    string s_tmp = s;
    if (s[i] == '0') {
      s_tmp[i] = '1';
      ll x = x_plus + modpow(2, n - 1 - i, div + 1);
      x %= div + 1;
      // debug(x);
      cout << f_(x) << endl;
    }
    if (s[i] == '1') {
      s_tmp[i] = '0';
      if (div - 1 == 0)
        cout << 0 << endl;
      else {
        ll x = x_minus - modpow(2, n - 1 - i, div - 1);
        if (x < 0)
          x += div - 1;
        x %= div - 1;
        // debug(x);
        cout << f_(x) << endl;
      }
    }
    // debug(s_tmp);
  }
}

Fixed submission:
#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define REP(i, n) for (int i = 1; i < (int)(n); i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define debug(var)                                                             \
  do {                                                                         \
    cout << #var << " : ";                                                     \
    view(var);                                                                 \
  } while (0)
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
using namespace std;
template <class T> void view(T e) { cout << e << endl; }
template <class T> void view(const vector<T> &v) {
  for (const auto &e : v) {
    cout << e << " ";
  }
  cout << endl;
}
template <class T> void view(const vector<vector<T>> &vv) {
  for (const auto &v : vv) {
    view(v);
  }
}
using vint = vector<int>;
using vvint = vector<vector<int>>;
using ll = long long;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
using P = pair<int, int>;
const int inf = 1e9;
const ll inf_l = 1e18;
const int MAX = 1e5;

long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}

int f(string s, int div) {
  int n = s.size();
  ll x = 0;
  rep(i, n) {
    if (s[i] == '1') {
      x += modpow(2, n - 1 - i, div);
      x %= div;
    }
  }
  return x % div;
}

int f_(int x, int ct = 1) {
  if (x == 0)
    return ct;
  int tmp = x % __builtin_popcount(x);
  if (tmp == 0)
    return ct + 1;
  return f_(tmp, ct + 1);
}

int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  int div = 0;
  rep(i, n) if (s[i] == '1') div++;
  int x_plus = f(s, div + 1);
  int x_minus = -1;
  if (div - 1 != 0)
    x_minus = f(s, div - 1);
  rep(i, n) {
    int div_tmp = div;
    string s_tmp = s;
    if (s[i] == '0') {
      s_tmp[i] = '1';
      ll x = x_plus + modpow(2, n - 1 - i, div + 1);
      x %= div + 1;
      // debug(x);
      cout << f_(x) << endl;
    }
    if (s[i] == '1') {
      s_tmp[i] = '0';
      if (div - 1 == 0)
        cout << 0 << endl;
      else {
        ll x = x_minus - modpow(2, n - 1 - i, div - 1);
        if (x < 0)
          x += div - 1;
        x %= div - 1;
        // debug(x);
        cout << f_(x) << endl;
      }
    }
    // debug(s_tmp);
  }
}