Problem p03899 (C++)

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

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define ll1 1ll
#define ONE 1ll
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T> void printvv(const vector<vector<T>> &v) {
  cerr << endl;
  rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
    if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
      cerr << "INF";
    } else
      cerr << v[i][j];
    cerr << (j == v[i].size() - 1 ? '\n' : ' ');
  }
  cerr << endl;
}
/*
typedef __int128_t Int;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
std::ostream::sentry s(dest);
  if (s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
          --d;
          *d = "0123456789"[tmp % 10];
          tmp /= 10;
        } while (tmp != 0);
        if (value < 0) {
          --d;
          *d = '-';
        }
        int len = std::end(buffer) - d;
        if (dest.rdbuf()->sputn(d, len) != len) {
          dest.setstate(std::ios_base::badbit);
        }
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
        if ('0' <= s[i] && s[i] <= '9')
          ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

signed main(signed argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  int N, M;
  cin >> N >> M;
  int K;
  cin >> K;
  vector<int> A(N);
  rep(i, 0, N) { cin >> A[i]; }
  vector<vector<int>> dp(K + 1, vector<int>(N + 2));
  rep(k, 1, K + 1) {
    rep(i, 0, N - k + 1) { dp[k][i] = dp[k - 1][i + 1] + (K - k + 1) * A[i]; }
    if (N == M) {
      rrep(i, 0, N) { chmax(dp[k][i], dp[k][i + 1]); }
    } else {
      priority_queue<pii, vector<pii>, less<pii>> pq;
      rep(i, 0, N - k + 1 + M) {
        if (i < M) {
          pq.push(pii(dp[k][i], i));
        } else {
          int j = i - M;
          while (pq.top().second < j)
            pq.pop();
          dp[k][j] = pq.top().first;
          if (i < N) {
            pq.push(pii(dp[k][i], i));
          }
        }
      }
    }
  }
  cout << *max_element(all(dp[K])) << endl;

  return 0;
}


Fixed submission:
#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define ll1 1ll
#define ONE 1ll
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
const double PI = acos(-1);
const double EPS = 1e-9;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>
istream &operator>>(istream &is, pair<T, S> &p) {
  is >> p.first >> p.second;
  return is;
}
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> &p) {
  os << p.first << " " << p.second;
  return os;
}

template <typename T> void printvv(const vector<vector<T>> &v) {
  cerr << endl;
  rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
    if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
      cerr << "INF";
    } else
      cerr << v[i][j];
    cerr << (j == v[i].size() - 1 ? '\n' : ' ');
  }
  cerr << endl;
}
/*
typedef __int128_t Int;
std::ostream &operator<<(std::ostream &dest, __int128_t value) {
std::ostream::sentry s(dest);
  if (s) {
        __uint128_t tmp = value < 0 ? -value : value;
        char buffer[128];
        char *d = std::end(buffer);
        do {
          --d;
          *d = "0123456789"[tmp % 10];
          tmp /= 10;
        } while (tmp != 0);
        if (value < 0) {
          --d;
          *d = '-';
        }
        int len = std::end(buffer) - d;
        if (dest.rdbuf()->sputn(d, len) != len) {
          dest.setstate(std::ios_base::badbit);
        }
  }
  return dest;
}

__int128 parse(string &s) {
  __int128 ret = 0;
  for (int i = 0; i < s.length(); i++)
        if ('0' <= s[i] && s[i] <= '9')
          ret = 10 * ret + s[i] - '0';
  return ret;
}
*/

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

signed main(signed argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);

  int N, M;
  cin >> N >> M;
  int K;
  cin >> K;
  vector<int> A(N);
  rep(i, 0, N) { cin >> A[i]; }
  vector<vector<int>> dp(K + 1, vector<int>(N + 2));
  rep(k, 1, K + 1) {
    rep(i, 0, N) { dp[k][i] = dp[k - 1][i + 1] + (K - k + 1) * A[i]; }
    deque<int> deq;
    rep(i, 0, N + M - 1) {
      if (i < N) {
        while (deq.size() and dp[k][deq.back()] <= dp[k][i])
          deq.pop_back();
        deq.push_back(i);
      }
      if (i - M + 1 >= 0) {
        dp[k][i - M + 1] = dp[k][deq.front()];
        if (deq.front() == i - M + 1)
          deq.pop_front();
      }
    }
  }
  cout << *max_element(all(dp[K])) << endl;

  return 0;
}