Problem p04016 (C++)

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

#define all(c) ((c).begin()), ((c).end())
#define dump(c) cerr << "> " << #c << " = " << (c) << endl;
#define iter(c) __typeof((c).begin())
#define tr(i, c) for (iter(c) i = (c).begin(); i != (c).end(); i++)
#define REP(i, a, b) for (int i = a; i < (int)(b); i++)
#define rep(i, n) REP(i, 0, n)
#define mp make_pair
#define fst first
#define snd second
#define pb push_back
#define debug(fmt, ...) fprintf(stderr, fmt "\n", ##__VA_ARGS__)

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int INF = 1 << 30;
const double EPS = 1e-10;

double zero(double d) { return d < EPS ? 0.0 : d; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  return os << '(' << p.first << ',' << p.second << ')';
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &a) {
  os << '[';
  rep(i, a.size()) os << (i ? " " : "") << a[i];
  return os << ']';
}

string toString(int i) {
  stringstream ss;
  ss << i;
  return ss.str();
}

const int MOD = 1000000007;
// a^k
ll fpow(ll a, ll k, int M) {
  ll res = 1ll;
  ll x = a;
  while (k != 0) {
    if ((k & 1) == 1)
      res = (res * x) % M;
    x = (x * x) % M;
    k >>= 1;
  }
  return res;
}

struct prepare {
  prepare() {
    cout.setf(ios::fixed, ios::floatfield);
    cout.precision(8);
    ios_base::sync_with_stdio(false);
  }
} _prepare;

ll dig(ll b, ll n) {
  ll ans = 0;
  while (n > 0) {
    if (n < b) {
      ans += n;
      break;
    }
    ans += (n % b);
    n /= b;
  }
  return ans;
}

int main() {
  ll n, s;
  cin >> n >> s;

  if (n == s) {
    cout << n + 1 << endl;
    return 0;
  }

  for (ll i = 2; i * i <= n; i++) {
    if (dig(i, n) == s) {
      cout << i << endl;
      return 0;
    }
  }

  ll ans = 1ll << 60;
  for (ll i = 1; i * i < n; i++) {
    if ((n - s) % i == 0) {
      ll b = (n - s) / i + 1;
      if (dig(b, n) == s)
        chmin(ans, b);
    }
  }

  if (ans != 1ll << 60) {
    cout << ans << endl;
  } else if (s == 1) {
    cout << n << endl;
  } else
    cout << -1 << endl;

  return 0;
}


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

#define all(c) ((c).begin()), ((c).end())
#define dump(c) cerr << "> " << #c << " = " << (c) << endl;
#define iter(c) __typeof((c).begin())
#define tr(i, c) for (iter(c) i = (c).begin(); i != (c).end(); i++)
#define REP(i, a, b) for (int i = a; i < (int)(b); i++)
#define rep(i, n) REP(i, 0, n)
#define mp make_pair
#define fst first
#define snd second
#define pb push_back
#define debug(fmt, ...) fprintf(stderr, fmt "\n", ##__VA_ARGS__)

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int INF = 1 << 30;
const double EPS = 1e-10;

double zero(double d) { return d < EPS ? 0.0 : d; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  return os << '(' << p.first << ',' << p.second << ')';
}

template <typename T> ostream &operator<<(ostream &os, const vector<T> &a) {
  os << '[';
  rep(i, a.size()) os << (i ? " " : "") << a[i];
  return os << ']';
}

string toString(int i) {
  stringstream ss;
  ss << i;
  return ss.str();
}

const int MOD = 1000000007;
// a^k
ll fpow(ll a, ll k, int M) {
  ll res = 1ll;
  ll x = a;
  while (k != 0) {
    if ((k & 1) == 1)
      res = (res * x) % M;
    x = (x * x) % M;
    k >>= 1;
  }
  return res;
}

struct prepare {
  prepare() {
    cout.setf(ios::fixed, ios::floatfield);
    cout.precision(8);
    ios_base::sync_with_stdio(false);
  }
} _prepare;

ll dig(ll b, ll n) {
  ll ans = 0;
  while (n > 0) {
    if (n < b) {
      ans += n;
      break;
    }
    ans += (n % b);
    n /= b;
  }
  return ans;
}

int main() {
  ll n, s;
  cin >> n >> s;

  if (n == s) {
    cout << n + 1 << endl;
    return 0;
  }

  for (ll i = 2; i * i <= n; i++) {
    if (dig(i, n) == s) {
      cout << i << endl;
      return 0;
    }
  }

  ll ans = 1ll << 60;
  for (ll i = 1; i * i < n; i++) {
    if (n - s >= 0 && (n - s) % i == 0) {
      ll b = ((n - s) / i) + 1;
      if (dig(b, n) == s)
        chmin(ans, b);
    }
  }

  if (ans != 1ll << 60) {
    cout << ans << endl;
  } else if (s == 1) {
    cout << n << endl;
  } else
    cout << -1 << endl;

  return 0;
}