Problem p03904 (C++)

Buggy submission (status: Memory Limit Exceeded):
#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rrep(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = (int)(s); i < (int)(t); ++i)
#define each(a, b) for (auto &(a) : (b))
#define all(v) (v).begin(), (v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define cmx(x, y) x = max(x, y)
#define cmn(x, y) x = min(x, y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout << #x << " = " << (x) << endl
#define spair(p) cout << #p << ": " << p.fi << " " << p.se << endl
#define sar(a, n)                                                              \
  cout << #a << ":";                                                           \
  rep(pachico, n) cout << " " << a[pachico];                                   \
  cout << endl
#define svec(v)                                                                \
  cout << #v << ":";                                                           \
  rep(pachico, v.size()) cout << " " << v[pachico];                            \
  cout << endl
#define svecp(v)                                                               \
  cout << #v << ":";                                                           \
  each(pachico, v) cout << " {" << pachico.first << ":" << pachico.second      \
                        << "}";                                                \
  cout << endl
#define sset(s)                                                                \
  cout << #s << ":";                                                           \
  each(pachico, s) cout << " " << pachico;                                     \
  cout << endl
#define smap(m)                                                                \
  cout << #m << ":";                                                           \
  each(pachico, m) cout << " {" << pachico.first << ":" << pachico.second      \
                        << "}";                                                \
  cout << endl

using namespace std;

typedef pair<int, int> P;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 100005;

string s;
int n, K, keta;

bool comp(string &a, string &b) {
  if (len(a) < len(b)) {
    return true;
  } else if (len(a) > len(b)) {
    return false;
  } else {
    return a < b;
  }
}

bool possible(string &t) {
  string nw;
  int cnt = 0;
  rep(i, n) {
    nw.pb(s[i]);
    if (comp(t, nw)) {
      nw.clear();
      cnt++;
      nw.pb(s[i]);
      if (comp(t, nw)) {
        return false;
      }
    }
  }
  return (cnt <= K);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> K;
  cin >> s;
  n = len(s);
  keta = (n + K) / (K + 1);
  vs ss;
  rep(i, n - keta + 1) { ss.pb(s.substr(i, keta)); }
  sort(all(ss), comp);
  int l = -1, r = n - keta;
  while (r - l > 1) {
    int mid = (l + r) / 2;
    if (possible(ss[mid])) {
      r = mid;
    } else {
      l = mid;
    }
  }
  cout << ss[r] << "\n";
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define rrep(i, n) for (int i = (int)(n)-1; i >= 0; --i)
#define srep(i, s, t) for (int i = (int)(s); i < (int)(t); ++i)
#define each(a, b) for (auto &(a) : (b))
#define all(v) (v).begin(), (v).end()
#define len(v) (int)(v).size()
#define zip(v) sort(all(v)), v.erase(unique(all(v)), v.end())
#define cmx(x, y) x = max(x, y)
#define cmn(x, y) x = min(x, y)
#define fi first
#define se second
#define pb push_back
#define show(x) cout << #x << " = " << (x) << endl
#define spair(p) cout << #p << ": " << p.fi << " " << p.se << endl
#define sar(a, n)                                                              \
  cout << #a << ":";                                                           \
  rep(pachico, n) cout << " " << a[pachico];                                   \
  cout << endl
#define svec(v)                                                                \
  cout << #v << ":";                                                           \
  rep(pachico, v.size()) cout << " " << v[pachico];                            \
  cout << endl
#define svecp(v)                                                               \
  cout << #v << ":";                                                           \
  each(pachico, v) cout << " {" << pachico.first << ":" << pachico.second      \
                        << "}";                                                \
  cout << endl
#define sset(s)                                                                \
  cout << #s << ":";                                                           \
  each(pachico, s) cout << " " << pachico;                                     \
  cout << endl
#define smap(m)                                                                \
  cout << #m << ":";                                                           \
  each(pachico, m) cout << " {" << pachico.first << ":" << pachico.second      \
                        << "}";                                                \
  cout << endl

using namespace std;

typedef pair<int, int> P;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<double> vd;
typedef vector<P> vp;
typedef vector<string> vs;

const int MAX_N = 100005;

string s;
int n, K, keta;

bool comp(string &a, string &b) {
  if (len(a) < len(b)) {
    return true;
  } else if (len(a) > len(b)) {
    return false;
  } else {
    return a < b;
  }
}

bool possible(string &t) {
  string nw;
  int cnt = 0;
  rep(i, n) {
    nw.pb(s[i]);
    if (comp(t, nw)) {
      nw.clear();
      cnt++;
      nw.pb(s[i]);
      if (comp(t, nw)) {
        return false;
      }
    }
  }
  return (cnt <= K);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> K;
  cin >> s;
  n = len(s);
  keta = (n + K) / (K + 1);
  if (K == 0) {
    cout << s << "\n";
    return 0;
  }
  if (K == 1) {
    string x = s.substr(0, keta), y = s.substr(n - keta, keta);
    if (comp(x, y)) {
      cout << y << "\n";
    } else {
      cout << x << "\n";
    }
    return 0;
  }
  vs ss;
  rep(i, n - keta + 1) { ss.pb(s.substr(i, keta)); }
  sort(all(ss), comp);
  int l = -1, r = n - keta;
  while (r - l > 1) {
    int mid = (l + r) / 2;
    if (possible(ss[mid])) {
      r = mid;
    } else {
      l = mid;
    }
  }
  cout << ss[r] << "\n";
  return 0;
}