Problem p01275 (C++) — buggy submission, verdict: Memory Limit Exceeded

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

#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;
  while (cin >> n && n) {
    string d(n, ' ');
    vector<char> x(n);
    rep(i, n) cin >> x[i];
    vector<char> y(n);
    rep(i, n) cin >> y[i];
    rep(i, n) {
      d[i] = (x[i] - y[i] < 0 ? x[i] - y[i] + 10 : x[i] - y[i]) + '0';
    }
    //        cout << d << endl;

    static queue<pair<string, ll>> q;
    static set<string> s;
    queue<pair<string, ll>>().swap(q);
    s.clear();

    q.push(mp(d, 0));
    int queue_max = 0;
    while (!q.empty()) {
      queue_max = max(queue_max, (int)q.size());
      auto tmp = q.front().fi;
      auto d = q.front().se;
      q.pop();
      //            cout << d << " " << tmp << endl;

      if (tmp == string(n, '0')) {
        cout << d << endl;
        //                cout << queue_max << "#MAX SIZE" << endl;
        goto next;
      }

      ll i = 0;
      while (tmp[i] == '0')
        i++;
      ll number = tmp[i] - '0';
      repi(j, i, n) {
        tmp[j] = '0' + ((tmp[j] - '0' - number) + 10) % 10;
        /*
        cout << j << " " << i << " " << number << endl;
        cout << tmp << endl;
        */
        if (!s.count(tmp)) {
          q.push(mp(tmp, d + 1));
          s.insert(tmp);
        }
      }
    }
  next:;
  }
  return 0;
}

Error: MLE

Fixed submission:

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

#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;
  while (cin >> n && n) {
    string d(n, ' ');
    vector<char> x(n);
    rep(i, n) cin >> x[i];
    vector<char> y(n);
    rep(i, n) cin >> y[i];
    rep(i, n) {
      d[i] = (x[i] - y[i] < 0 ? x[i] - y[i] + 10 : x[i] - y[i]) + '0';
    }
    //        cout << d << endl;

    static queue<pair<string, ll>> q;
    queue<pair<string, ll>>().swap(q);
    q.push(mp(d, 0));
    while (!q.empty()) {
      auto tmp = q.front().fi;
      auto d = q.front().se;
      q.pop();
      //            cout << d << " " << tmp << endl;

      if (tmp == string(n, '0')) {
        cout << d << endl;
        goto next;
      }

      ll i = 0;
      while (tmp[i] == '0')
        i++;
      ll number = tmp[i] - '0';
      repi(j, i, n) {
        tmp[j] = '0' + ((tmp[j] - '0' - number) + 10) % 10;
        /*
        cout << j << " " << i << " " << number << endl;
        cout << tmp << endl;
        */
        q.push(mp(tmp, d + 1));
      }
    }
  next:;
  }
  return 0;
}