Problem p03355 (C++)

Buggy submission (status: Time Limit Exceeded):

#define _CRT_SECURE_NO_WARNINGS

#include <algorithm>
#include <cmath>
#include <ctime>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

#define endl "\n"
#define X first
#define Y second
#define Z third
#define mp make_pair
#define mt make_triple

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

const ld PI = 3.141592653589793;
const ld E = 2.71828182845904523;
const ll LLINF = 4000000009000000099;
const ll INF = 1009000099;
const ll MOD7 = 1000000007;
const ll MOD9 = 1000000009;

template <class A, class B, class C> struct triple {
  A first;
  B second;
  C third;
  triple(A, B, C);
  triple();
};
template <class A, class B, class C> triple<A, B, C>::triple(A a, B b, C c) {
  first = a;
  second = b;
  third = c;
}
template <class A, class B, class C> triple<A, B, C>::triple() {}
template <class A, class B, class C>
triple<A, B, C> make_triple(A a, B b, C c) {
  triple<A, B, C> t(a, b, c);
  return t;
}
template <class A, class B, class C>
bool operator<(triple<A, B, C> a, triple<A, B, C> b) {
  if (a.first != b.first)
    return a.first < b.first;
  if (a.second != b.second)
    return a.second < b.second;
  if (a.third != b.third)
    return a.third < b.third;
}
template <class T> T inline sqr(T a) { return a * a; }

ll bpow(ll a, ll d, ll mod) {
  if (d == 0)
    return 1;
  ll t = bpow(a, d / 2, mod);
  t = (t * t) % mod;
  if (d & 1)
    t = (t * a) % mod;
  return t;
}
ll bpow(ll a, ll d) {
  if (d == 0)
    return 1;
  ll t = bpow(a, d / 2);
  t = (t * t);
  if (d & 1)
    t = (t * a);
  return t;
}
ll gcd(ll a, ll b) {
  while (a && b)
    if (a > b)
      a %= b;
    else
      b %= a;
  return a + b;
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
ll C(ll n, ll k) {
  ll res = 1;
  for (int i = 1; i <= k; ++i)
    res = res * (n - k + i) / i;
  return res;
}
ll C(ll n, ll k, ll mod) {
  ll u = 1, d = 1;
  for (int i = 2; i <= n; ++i)
    u = (u * i) % mod;
  int x = max(k, n - k), z = min(k, n - k);
  for (int i = 2; i <= x; ++i) {
    d = (d * i) % mod;
    if (i <= z)
      d = (d * i) % mod;
  }
  d = bpow(d, mod - 2, mod);
  ll res = (u * d) % mod;
  return res;
}

bool cmp(string a, string b) {
  for (int i = 0; i < min(a.length(), b.length()); ++i)
    if (a[i] != b[i])
      return a[i] < b[i];

  return a.length() < b.length();
}

void solve() {
  string s;
  cin >> s;
  int n = s.length();
  int k;
  cin >> k;
  set<string> p;
  vector<string> v;
  string tmp = s;
  sort(tmp.begin(), tmp.end());

  for (int i = 0; i < n && p.size() <= 5; ++i)
    if (!i || tmp[i] != tmp[i - 1]) {

      for (int j = 0; j < n; ++j)
        if (s[j] == tmp[i]) {
          string cur = "";
          for (int k = j; k < n; ++k) {
            cur += s[k];
            p.insert(cur);
          }
        }
    }

  for (auto it = p.begin(); it != p.end(); ++it)
    v.push_back(*it);

  sort(v.begin(), v.end(), cmp);

  cout << v[k - 1];
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
#ifdef _DEBUG
  freopen("in.txt", "r", stdin);
#else
#endif
  solve();
  return 0;
}

Fixed submission:

#define _CRT_SECURE_NO_WARNINGS

#include <algorithm>
#include <cmath>
#include <ctime>
#include <deque>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

#define endl "\n"
#define X first
#define Y second
#define Z third
#define mp make_pair
#define mt make_triple

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

const ld PI = 3.141592653589793;
const ld E = 2.71828182845904523;
const ll LLINF = 4000000009000000099;
const ll INF = 1009000099;
const ll MOD7 = 1000000007;
const ll MOD9 = 1000000009;

template <class A, class B, class C> struct triple {
  A first;
  B second;
  C third;
  triple(A, B, C);
  triple();
};
template <class A, class B, class C> triple<A, B, C>::triple(A a, B b, C c) {
  first = a;
  second = b;
  third = c;
}
template <class A, class B, class C> triple<A, B, C>::triple() {}
template <class A, class B, class C>
triple<A, B, C> make_triple(A a, B b, C c) {
  triple<A, B, C> t(a, b, c);
  return t;
}
template <class A, class B, class C>
bool operator<(triple<A, B, C> a, triple<A, B, C> b) {
  if (a.first != b.first)
    return a.first < b.first;
  if (a.second != b.second)
    return a.second < b.second;
  if (a.third != b.third)
    return a.third < b.third;
}
template <class T> T inline sqr(T a) { return a * a; }

ll bpow(ll a, ll d, ll mod) {
  if (d == 0)
    return 1;
  ll t = bpow(a, d / 2, mod);
  t = (t * t) % mod;
  if (d & 1)
    t = (t * a) % mod;
  return t;
}
ll bpow(ll a, ll d) {
  if (d == 0)
    return 1;
  ll t = bpow(a, d / 2);
  t = (t * t);
  if (d & 1)
    t = (t * a);
  return t;
}
ll gcd(ll a, ll b) {
  while (a && b)
    if (a > b)
      a %= b;
    else
      b %= a;
  return a + b;
}
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
ll C(ll n, ll k) {
  ll res = 1;
  for (int i = 1; i <= k; ++i)
    res = res * (n - k + i) / i;
  return res;
}
ll C(ll n, ll k, ll mod) {
  ll u = 1, d = 1;
  for (int i = 2; i <= n; ++i)
    u = (u * i) % mod;
  int x = max(k, n - k), z = min(k, n - k);
  for (int i = 2; i <= x; ++i) {
    d = (d * i) % mod;
    if (i <= z)
      d = (d * i) % mod;
  }
  d = bpow(d, mod - 2, mod);
  ll res = (u * d) % mod;
  return res;
}

bool cmp(string a, string b) {
  for (int i = 0; i < min(a.length(), b.length()); ++i)
    if (a[i] != b[i])
      return a[i] < b[i];

  return a.length() < b.length();
}

void solve() {
  string s;
  cin >> s;
  int n = s.length();
  int k;
  cin >> k;
  set<string> p;
  vector<string> v;
  string tmp = s;
  sort(tmp.begin(), tmp.end());

  for (int i = 0; i < n && p.size() <= 5; ++i)
    if (!i || tmp[i] != tmp[i - 1]) {

      for (int j = 0; j < n; ++j)
        if (s[j] == tmp[i]) {
          string cur = "";
          for (int k = j; k < n && k - j < 7; ++k) {
            cur += s[k];
            p.insert(cur);
          }
        }
    }

  for (auto it = p.begin(); it != p.end(); ++it)
    v.push_back(*it);

  sort(v.begin(), v.end(), cmp);

  cout << v[k - 1];
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
#ifdef _DEBUG
  freopen("in.txt", "r", stdin);
#else
#endif
  solve();
  return 0;
}