Problem p04016 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

#ifdef _WIN32
#define scanfll(x) scanf("%I64d", x)
#define printfll(x) printf("%I64d", x)
#else
#define scanfll(x) scanf("%lld", x)
#define printfll(x) printf("%lld", x)
#endif
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define repi(i, a, b)                                                          \
  for (long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template <class T1, class T2> bool chmin(T1 &a, T2 b) {
  return b < a && (a = b, true);
}
template <class T1, class T2> bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

using ll = long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vi = vector<int>;
using vvi = vector<vi>;
vll conv(vi &v) {
  vll r(v.size());
  rep(i, v.size()) r[i] = v[i];
  return r;
}
using P = pair<ll, ll>;

template <typename T, typename U>
ostream &operator<<(ostream &o, const pair<T, U> &v) {
  o << "(" << v.first << ", " << v.second << ")";
  return o;
}
template <size_t...> struct seq {};
template <size_t N, size_t... Is>
struct gen_seq : gen_seq<N - 1, N - 1, Is...> {};
template <size_t... Is> struct gen_seq<0, Is...> : seq<Is...> {};
template <class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch, Tr> &os, Tuple const &t, seq<Is...>) {
  using s = int[];
  (void)s{0, (void(os << (Is == 0 ? "" : ", ") << get<Is>(t)), 0)...};
}
template <class Ch, class Tr, class... Args>
auto operator<<(basic_ostream<Ch, Tr> &os, tuple<Args...> const &t)
    -> basic_ostream<Ch, Tr> & {
  os << "(";
  print_tuple(os, t, gen_seq<sizeof...(Args)>());
  return os << ")";
}
ostream &operator<<(ostream &o, const vvll &v) {
  rep(i, v.size()) {
    rep(j, v[i].size()) o << v[i][j] << " ";
    cout << endl;
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const unordered_map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it;
  o << "]";
  return o;
}
void printbits(ll mask, ll n) {
  rep(i, n) { cout << !!(mask & (1ll << i)); }
  cout << endl;
}
#define ldout fixed << setprecision(40)

static const double EPS = 1e-14;
static const long long INF = 1e18;
static const long long mo = 1e9 + 7;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, s;
  cin >> n >> s;
  if (n < s) {
    cout << -1 << endl;
    return 0;
  }

  ll ret = INF;

  // k = 1
  if (n == s) {
    chmin(ret, n + 1);
  }

  // k = 2
  repi(p, 1, 1000000) {
    if ((n - s) % p != 0)
      continue;
    vll cand = {(n - s) / p + 1, p + 1};
    for (ll b : cand) {
      if ((n - s) % (b - 1) == 0) {
        ll a1 = (n - s) / (b - 1);
        ll a0 = s - a1;
        if (a0 >= 0 && a1 >= 0 && b > a0 && b > a1 && n == a0 + a1 * b) {
          chmin(ret, b);
          //                    cout << b << " " << a0 << " " << a1 << " " <<
          //                    "#hit" << endl;
        }
      }
    }
  }

  // k > 2
  repi(b, 2, 1000000) {
    ll tmp = n;
    vll a;
    while (tmp) {
      a.pb(tmp % b);
      tmp /= b;
    }
    ll check = 0;
    rep(i, a.size()) { check += a[i]; }
    if (s == check) {
      //            cout << b << " " << a << endl;
      chmin(ret, b);
    }
  }
  if (ret == INF)
    cout << -1 << endl;
  else
    cout << ret << endl;
  return 0;
}


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

#ifdef _WIN32
#define scanfll(x) scanf("%I64d", x)
#define printfll(x) printf("%I64d", x)
#else
#define scanfll(x) scanf("%lld", x)
#define printfll(x) printf("%lld", x)
#endif
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define repi(i, a, b)                                                          \
  for (long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template <class T1, class T2> bool chmin(T1 &a, T2 b) {
  return b < a && (a = b, true);
}
template <class T1, class T2> bool chmax(T1 &a, T2 b) {
  return a < b && (a = b, true);
}

using ll = long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using vld = vector<ld>;
using vi = vector<int>;
using vvi = vector<vi>;
vll conv(vi &v) {
  vll r(v.size());
  rep(i, v.size()) r[i] = v[i];
  return r;
}
using P = pair<ll, ll>;

template <typename T, typename U>
ostream &operator<<(ostream &o, const pair<T, U> &v) {
  o << "(" << v.first << ", " << v.second << ")";
  return o;
}
template <size_t...> struct seq {};
template <size_t N, size_t... Is>
struct gen_seq : gen_seq<N - 1, N - 1, Is...> {};
template <size_t... Is> struct gen_seq<0, Is...> : seq<Is...> {};
template <class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch, Tr> &os, Tuple const &t, seq<Is...>) {
  using s = int[];
  (void)s{0, (void(os << (Is == 0 ? "" : ", ") << get<Is>(t)), 0)...};
}
template <class Ch, class Tr, class... Args>
auto operator<<(basic_ostream<Ch, Tr> &os, tuple<Args...> const &t)
    -> basic_ostream<Ch, Tr> & {
  os << "(";
  print_tuple(os, t, gen_seq<sizeof...(Args)>());
  return os << ")";
}
ostream &operator<<(ostream &o, const vvll &v) {
  rep(i, v.size()) {
    rep(j, v[i].size()) o << v[i][j] << " ";
    cout << endl;
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  o << '[';
  rep(i, v.size()) o << v[i] << (i != v.size() - 1 ? ", " : "");
  o << "]";
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it << (next(it) != m.end() ? ", " : "");
  o << "]";
  return o;
}
template <typename T, typename U>
ostream &operator<<(ostream &o, const unordered_map<T, U> &m) {
  o << '[';
  for (auto it = m.begin(); it != m.end(); it++)
    o << *it;
  o << "]";
  return o;
}
void printbits(ll mask, ll n) {
  rep(i, n) { cout << !!(mask & (1ll << i)); }
  cout << endl;
}
#define ldout fixed << setprecision(40)

static const double EPS = 1e-14;
static const long long INF = 1e18;
static const long long mo = 1e9 + 7;

int main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll n, s;
  cin >> n >> s;
  if (n < s) {
    cout << -1 << endl;
    return 0;
  }

  ll ret = INF;

  // k = 1
  if (n == s) {
    chmin(ret, n + 1);
  }

  // k = 2
  repi(p, 1, 1000000) {
    if ((n - s) % p != 0)
      continue;
    vll cand = {(n - s) / p + 1, p + 1};
    for (ll b : cand) {
      if (b < 2)
        continue;
      if ((n - s) % (b - 1) == 0) {
        ll a1 = (n - s) / (b - 1);
        ll a0 = s - a1;
        if (a0 >= 0 && a1 >= 0 && b > a0 && b > a1 && n == a0 + a1 * b) {
          chmin(ret, b);
          //                    cout << b << " " << a0 << " " << a1 << " " <<
          //                    "#hit" << endl;
        }
      }
    }
  }

  // k > 2
  repi(b, 2, 1000000) {
    ll tmp = n;
    vll a;
    while (tmp) {
      a.pb(tmp % b);
      tmp /= b;
    }
    ll check = 0;
    rep(i, a.size()) { check += a[i]; }
    if (s == check) {
      //            cout << b << " " << a << endl;
      chmin(ret, b);
    }
  }
  if (ret == INF)
    cout << -1 << endl;
  else
    cout << ret << endl;
  return 0;
}