Problem p02127 (C++) — buggy submission, verdict: Memory Limit Exceeded

#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll LLINF = (1LL << 60);
const int INF = (1LL << 30);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a <= x && x < b; }
template <typename T> T ceil(T a, T b) { return a / b + !!(a % b); }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &a) {
  out << '(' << a.first << ',' << a.second << ')';
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << '[';
  REP(i, a.size()) {
    out << a[i];
    if (i != a.size() - 1)
      out << ',';
  }
  out << ']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  string s, t;
  cin >> s >> t;

  string now = t;
  REP(i, 30) {
    // sの中にnowが含まれるか判定
    int cnt = 0;
    REP(j, s.size()) if (cnt < now.size() && s[j] == now[cnt]) cnt++;
    if (cnt < now.size()) {
      cout << i << endl;
      return 0;
    }
    int n_sz = now.size() * t.size() + now.size() + t.size();
    if (n_sz > s.size()) {
      cout << i + 1 << endl;
      return 0;
    }
    string n = now;
    REP(j, t.size()) n += t[j] + now;
    now = n;
  }

  return 0;
}


Error: MLE

Fixed submission:

#define __USE_MINGW_ANSI_STDIO 0
#include <bits/stdc++.h>

using namespace std;
using ll = long long;
#define int ll
using VI = vector<int>;
using VVI = vector<VI>;
using PII = pair<int, int>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define PB push_back

const ll LLINF = (1LL << 60);
const int INF = (1LL << 30);
const int MOD = 1000000007;

template <typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template <typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template <typename T> bool IN(T a, T b, T x) { return a <= x && x < b; }
template <typename T> T ceil(T a, T b) { return a / b + !!(a % b); }
template <class S, class T>
ostream &operator<<(ostream &out, const pair<S, T> &a) {
  out << '(' << a.first << ',' << a.second << ')';
  return out;
}
template <class T> ostream &operator<<(ostream &out, const vector<T> &a) {
  out << '[';
  REP(i, a.size()) {
    out << a[i];
    if (i != a.size() - 1)
      out << ',';
  }
  out << ']';
  return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  string s, t;
  cin >> s >> t;

  string now = t;
  REP(i, 30) {
    // sの中にnowが含まれるか判定
    int cnt = 0;
    REP(j, s.size()) if (cnt < now.size() && s[j] == now[cnt]) cnt++;
    if (cnt < now.size()) {
      cout << i << endl;
      return 0;
    }
    string n = now;
    REP(j, t.size()) n += t[j] + now;
    now = n;
  }

  return 0;
}