Problem p03355 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<ll, ll> pl;
typedef vector<pl> vp;
const ll INF = 1001001001;
const ll LINF = 1001001001001001001;
const ll D4[] = {0, 1, 0, -1, 0};
const ll D8[] = {0, 1, 1, 0, -1, -1, 1, -1, 0};
#define _overload3(_1, _2, _3, name, ...) name
#define _rep2(i, n) for (ll i = 0; i < (n); ++i)
#define _rep3(i, a, b) for (ll i = (a); i < (b); ++i)
#define rep(...) _overload3(__VA_ARGS__, _rep3, _rep2)(__VA_ARGS__)
#define _repe2(i, n) for (ll i = 0; i <= (n); ++i)
#define _repe3(i, a, b) for (ll i = (a); i <= (b); ++i)
#define repe(...) _overload3(__VA_ARGS__, _repe3, _repe2)(__VA_ARGS__)
#define _rrep2(i, n) for (ll i = (n)-1; i >= 0; i--)
#define _rrep3(i, a, b) for (ll i = (b)-1; i >= (a); i--)
#define rrep(...) _overload3(__VA_ARGS__, _rrep3, _rrep2)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> using pq = priority_queue<T, vector<T>, greater<T>>;

string s;
ll K;

void solve();

int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cin >> s;
  cin >> K;
  solve();
}

// 1 ≤ |s| ≤ 5000
// s は英小文字からなる
// 1 ≤ K ≤ 5
// s は異なる substring を K 個以上持つ

// string s, ll K
// 辞書順で K 番目に小さい s の substring を出力せよ。
void solve() {
  ll n = s.size();
  set<string> st;
  rep(i, n) repe(j, 1, n - i) { st.insert(s.substr(i, j)); }

  ll id = 1;
  for (string ss : st) {
    if (id == K) {
      cout << ss << endl;
      return;
    }
    ++id;
  }
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<ll, ll> pl;
typedef vector<pl> vp;
const ll INF = 1001001001;
const ll LINF = 1001001001001001001;
const ll D4[] = {0, 1, 0, -1, 0};
const ll D8[] = {0, 1, 1, 0, -1, -1, 1, -1, 0};
#define _overload3(_1, _2, _3, name, ...) name
#define _rep2(i, n) for (ll i = 0; i < (n); ++i)
#define _rep3(i, a, b) for (ll i = (a); i < (b); ++i)
#define rep(...) _overload3(__VA_ARGS__, _rep3, _rep2)(__VA_ARGS__)
#define _repe2(i, n) for (ll i = 0; i <= (n); ++i)
#define _repe3(i, a, b) for (ll i = (a); i <= (b); ++i)
#define repe(...) _overload3(__VA_ARGS__, _repe3, _repe2)(__VA_ARGS__)
#define _rrep2(i, n) for (ll i = (n)-1; i >= 0; i--)
#define _rrep3(i, a, b) for (ll i = (b)-1; i >= (a); i--)
#define rrep(...) _overload3(__VA_ARGS__, _rrep3, _rrep2)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> using pq = priority_queue<T, vector<T>, greater<T>>;

string s;
ll K;

void solve();

int main() {
  cin.tie(0);
  ios::sync_with_stdio(0);
  cin >> s;
  cin >> K;
  solve();
}

// 1 ≤ |s| ≤ 5000
// s は英小文字からなる
// 1 ≤ K ≤ 5
// s は異なる substring を K 個以上持つ

// string s, ll K
// 辞書順で K 番目に小さい s の substring を出力せよ。
void solve() {
  ll n = s.size();
  set<string> st;
  rep(i, n) repe(j, 1, n - i) {
    if (j > 5)
      break;
    st.insert(s.substr(i, j));
  }

  ll id = 1;
  for (string ss : st) {
    if (id == K) {
      cout << ss << endl;
      return;
    }
    ++id;
  }
}