Problem p03353 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#include <cmath>
#include <math.h>

using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using vvs = vector<vs>;
using vc = vector<char>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;

#define rep(i, n)                                                              \
  ;                                                                            \
  for (int i = 0; i < n; i++)
#define all(a) a.begin(), a.end()
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n", a)
#define mem(a) memset(a, 0, sizeof(a))
#define f(i, a, b) for (int i = a; i < b; i++)
#define pri(a) printf("%.14lf\n", a);
#define MOD 1000000007
typedef pair<int, int> P;
bool is_int_lround(double x) { return std::lround(x) == x; }
ll keta(ll x) {
  ll n = 0;
  while (x > 0) {
    x /= 10;
    n++;
  }
  return n;
}

ll conbi(int n, int m) {

  cin >> n >> m;
  vector<ll> a(100);
  a[0] = 1;
  for (int i = 0; i < 14; i++) {
    a[i + 1] = a[i] * (i + 1);
  }
  return a[n] / (a[m] * a[n - m]);
}

long long modpow(long long a, long long n, long long mod) {
  long long res = 1; // 繰り返し二乗法
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
ll kaijo(ll x) {
  ll z = 1;
  while (x > 0) {
    z *= x;
    z %= MOD;
    x--;
  }
  return z;
}
ll yakusu_num(ll n) {
  vl yakusu(n + 1, 1);
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      n /= i;
      yakusu[i]++;
    }
  }
  if (n != 1)
    yakusu[n]++;
  ll num = 1;
  for (ll i = 0; i <= n; i++) {
    num *= yakusu[i];
  }
  return num;
}

// cout<<""<<endl;
int main() {
  string S;
  int K;
  cin >> S >> K;
  map<string, int> mp;
  for (int k = 1; k <= S.size(); k++) {
    for (int i = 0; i + k - 1 < S.size(); i++) {
      mp[S.substr(i, k)]++;
    }
  }
  int r = 1;
  for (auto x : mp) {
    if (r == K)
      cout << x.first << endl;
    r++;
  }
}


Fixed submission:
#include <bits/stdc++.h>
#include <cmath>
#include <math.h>

using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using vvs = vector<vs>;
using vc = vector<char>;
using vvc = vector<vc>;
using vb = vector<bool>;
using vvb = vector<vb>;

#define rep(i, n)                                                              \
  ;                                                                            \
  for (int i = 0; i < n; i++)
#define all(a) a.begin(), a.end()
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n", a)
#define mem(a) memset(a, 0, sizeof(a))
#define f(i, a, b) for (int i = a; i < b; i++)
#define pri(a) printf("%.14lf\n", a);
#define MOD 1000000007
typedef pair<int, int> P;
bool is_int_lround(double x) { return std::lround(x) == x; }
ll keta(ll x) {
  ll n = 0;
  while (x > 0) {
    x /= 10;
    n++;
  }
  return n;
}

ll conbi(int n, int m) {

  cin >> n >> m;
  vector<ll> a(100);
  a[0] = 1;
  for (int i = 0; i < 14; i++) {
    a[i + 1] = a[i] * (i + 1);
  }
  return a[n] / (a[m] * a[n - m]);
}

long long modpow(long long a, long long n, long long mod) {
  long long res = 1; // 繰り返し二乗法
  while (n > 0) {
    if (n & 1)
      res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
ll kaijo(ll x) {
  ll z = 1;
  while (x > 0) {
    z *= x;
    z %= MOD;
    x--;
  }
  return z;
}
ll yakusu_num(ll n) {
  vl yakusu(n + 1, 1);
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      n /= i;
      yakusu[i]++;
    }
  }
  if (n != 1)
    yakusu[n]++;
  ll num = 1;
  for (ll i = 0; i <= n; i++) {
    num *= yakusu[i];
  }
  return num;
}

// cout<<""<<endl;
int main() {
  string S;
  int K;
  cin >> S >> K;
  map<string, int> mp;
  for (int k = 1; k <= 5; k++) {
    for (int i = 0; i + k - 1 < S.size(); i++) {
      mp[S.substr(i, k)]++;
    }
  }
  int r = 1;
  for (auto x : mp) {
    if (r == K)
      cout << x.first << endl;
    r++;
  }
}