Problem p03202 (C++)

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

using namespace std;
#define _USE_MATH_DEFINES_
#define ll long long
#define ld long double
#define Accepted 0
#define pb push_back
#define mp make_pair
#define sz(x) (int)(x.size())
#define every(x) x.begin(), x.end()
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define For(i, x, y) for (ll i = x; i <= y; i++)
#define FOr(i, x, y) for (ll i = x; i >= y; i--)
#define SpeedForce ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
// ROAD to... Red

inline void Input_Output() {
  // freopen(".in", "r", stdin);
  // freopen(".out", "w", stdout);
}

const double eps = 0.000001;
const ld pi = acos(-1);
const int maxn = 1e7 + 9;
const int mod = 1e9 + 7;
const ll MOD = 1e18 + 9;
const ll INF = 1e18 + 123;
const int inf = 2e9 + 11;
const int mxn = 1e6 + 9;
const int N = 6e5 + 123;
const int M = 22;
const int pri = 997;
const int Magic = 2101;

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

int n, m, k;
int a[N];

bool check(int x) {
  map<int, int> s;
  for (int i = 2; i <= n; i++) {
    if (a[i] > a[i - 1])
      continue;
    if (s.upper_bound(a[i]) != s.end()) {
      s.erase(s.upper_bound(a[i]));
    }
    int k = a[i];
    s[k]++;

    while (k > 0 && s[k] == x)
      s.erase(k), s[--k]++;
    if (k == 0)
      return 0;
  }
  return 1;
}

int main() {
  SpeedForce;
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }

  int l = 0, r = 1e9 + 1;
  while (r - l > 1) {
    int md = (l + r) >> 1;
    if (check(md))
      r = md;
    else
      l = md;
  }
  assert(r != 1e9 + 1);

  cout << r << '\n';
  return Accepted;
}

// B...a

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

using namespace std;
#define _USE_MATH_DEFINES_
#define ll long long
#define ld long double
#define Accepted 0
#define pb push_back
#define mp make_pair
#define sz(x) (int)(x.size())
#define every(x) x.begin(), x.end()
#define F first
#define S second
#define lb lower_bound
#define ub upper_bound
#define For(i, x, y) for (ll i = x; i <= y; i++)
#define FOr(i, x, y) for (ll i = x; i >= y; i--)
#define SpeedForce ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
// ROAD to... Red

inline void Input_Output() {
  // freopen(".in", "r", stdin);
  // freopen(".out", "w", stdout);
}

const double eps = 0.000001;
const ld pi = acos(-1);
const int maxn = 1e7 + 9;
const int mod = 1e9 + 7;
const ll MOD = 1e18 + 9;
const ll INF = 1e18 + 123;
const int inf = 2e9 + 11;
const int mxn = 1e6 + 9;
const int N = 6e5 + 123;
const int M = 22;
const int pri = 997;
const int Magic = 2101;

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

int n, m, k;
int a[N];

bool check(int x) {
  if (x == 1)
    return is_sorted(a + 1, a + n + 1);

  map<int, int> s;
  for (int i = 2; i <= n; i++) {
    if (a[i] > a[i - 1])
      continue;
    if (s.upper_bound(a[i]) != s.end()) {
      s.erase(s.upper_bound(a[i]));
    }
    int k = a[i];
    s[k]++;

    while (k > 0 && s[k] == x)
      s.erase(k), s[--k]++;
    if (k == 0)
      return 0;
  }
  return 1;
}

int main() {
  SpeedForce;
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
  }

  int l = 0, r = 1e9 + 1;
  while (r - l > 1) {
    int md = (l + r) >> 1;
    if (check(md))
      r = md;
    else
      l = md;
  }
  assert(r != 1e9 + 1);

  cout << r << '\n';
  return Accepted;
}

// B...a