Problem p02702 (C++) — buggy submission, verdict: Memory Limit Exceeded

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <climits>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#define LEN(x) (long long)(x.size())
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define FOE(i, a) for (auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
#define IS_BIT_ON(bit, i) (bit & (1 << i))
#define BIT_ON(bit, i) (bit |= (1 << i))
#define BIT_OFF(bit, i) (bit &= ~(1 << i))
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;

template <typename T> std::vector<T> make_v(size_t a) {
  return std::vector<T>(a);
}

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return std::vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
} // C++14
template <typename T, typename V>
typename std::enable_if<std::is_class<T>::value == 0>::type fill_v(T &t,
                                                                   const V &v) {
  t = v;
}

template <typename T, typename V>
typename std::enable_if<std::is_class<T>::value != 0>::type fill_v(T &t,
                                                                   const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

template <class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }

void print() { std::cout << std::endl; }

template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  std::cout << head;
  if (sizeof...(tail) != 0) {
    std::cout << " ";
  }
  print(std::forward<Tail>(tail)...);
}

template <class T> void print(std::vector<T> &v) {
  for (auto &a : v) {
    std::cout << a;
    if (&a != &v.back()) {
      std::cout << " ";
    }
  }
  std::cout << std::endl;
}

template <class T> void print(std::vector<std::vector<T>> &vv) {
  for (auto &v : vv) {
    print(v);
  }
}

void debug() { std::cerr << std::endl; }

template <class Head, class... Tail> void debug(Head &&head, Tail &&...tail) {
  std::cerr << head;
  if (sizeof...(tail) != 0) {
    std::cerr << " ";
  }
  print(std::forward<Tail>(tail)...);
}

template <class T> void debug(std::vector<T> &v) {
  for (auto &a : v) {
    std::cerr << a;
    if (&a != &v.back()) {
      std::cerr << " ";
    }
  }
  std::cerr << std::endl;
}

template <class T> void debug(std::vector<std::vector<T>> &vv) {
  for (auto &v : vv) {
    print(v);
  }
}

inline bool inside(long long y, long long x, long long H, long long W) {
  return 0 <= y and y < H and 0 <= x and x < W;
}

template <class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) {
  return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

template <class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) {
  return abs(x1 - x2) + abs(y1 - y2);
}

template <typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }

template <typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template <class T> inline std::vector<T> unique(std::vector<T> v) {
  sort(v.begin(), v.end());
  v.erase(unique(v.begin(), v.end()), v.end());
  return v;
}

long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
  return n * (2 * s + (n - 1) * d) / 2;
}

bool is_power_of_two(long long x) { return !(x & (x - 1)); }

long long gcd(long long a, long long b) {
  if (b == 0) {
    return a;
  }
  return gcd(b, a % b);
}

long long gcd(std::vector<long long> &v) {
  long long ans = v[0];
  for (int i = 1; i < (int)v.size(); ++i) {
    ans = gcd(ans, v[i]);
  }
  return ans;
}

long long lcm(long long a, long long b) {
  long long g = gcd(a, b);
  return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 58u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};
const std::vector<int> dy8 = {0, -1, 0, 1, 1, -1, -1, 1},
                       dx8 = {1, 0, -1, 0, 1, 1, -1, -1};

using namespace std;

int main(int argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  string S;
  cin >> S;
  const int N = LEN(S);

  auto dp = make_v<int>(2, 2020);
  dp[0][0] = 1;

  LL ans = 0;
  FOR(i, 0, N) {
    const int d = S[i] - '0';
    fill_v(dp[(i + 1) % 2], 0);

    if (i != 0) {
      dp[(i + 1) % 2][d % 2019] += 1;
    }

    FOR(j, 0, 2020) {
      if (dp[i % 2][j] == 0) {
        continue;
      }

      dp[(i + 1) % 2][(j * 10 + d) % 2019] += dp[i % 2][j];
    }

    if (i != 0) {
      ans += dp[i % 2][0];
    }
  }

  ans += dp[N % 2][0];
  print(ans);

  return 0;
}

Error: MLE

Fixed submission:

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <climits>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#define LEN(x) (long long)(x.size())
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define FOE(i, a) for (auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
#define IS_BIT_ON(bit, i) (bit & (1 << i))
#define BIT_ON(bit, i) (bit |= (1 << i))
#define BIT_OFF(bit, i) (bit &= ~(1 << i))
#define BIT_COUNT(bit) (__builtin_popcount(bit))

typedef long long LL;

template <typename T> std::vector<T> make_v(size_t a) {
  return std::vector<T>(a);
}

template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) {
  return std::vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
} // C++14
template <typename T, typename V>
typename std::enable_if<std::is_class<T>::value == 0>::type fill_v(T &t,
                                                                   const V &v) {
  t = v;
}

template <typename T, typename V>
typename std::enable_if<std::is_class<T>::value != 0>::type fill_v(T &t,
                                                                   const V &v) {
  for (auto &e : t)
    fill_v(e, v);
}

template <class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }

void print() { std::cout << std::endl; }

template <class Head, class... Tail> void print(Head &&head, Tail &&...tail) {
  std::cout << head;
  if (sizeof...(tail) != 0) {
    std::cout << " ";
  }
  print(std::forward<Tail>(tail)...);
}

template <class T> void print(std::vector<T> &v) {
  for (auto &a : v) {
    std::cout << a;
    if (&a != &v.back()) {
      std::cout << " ";
    }
  }
  std::cout << std::endl;
}

template <class T> void print(std::vector<std::vector<T>> &vv) {
  for (auto &v : vv) {
    print(v);
  }
}

void debug() { std::cerr << std::endl; }

template <class Head, class... Tail> void debug(Head &&head, Tail &&...tail) {
  std::cerr << head;
  if (sizeof...(tail) != 0) {
    std::cerr << " ";
  }
  print(std::forward<Tail>(tail)...);
}

template <class T> void debug(std::vector<T> &v) {
  for (auto &a : v) {
    std::cerr << a;
    if (&a != &v.back()) {
      std::cerr << " ";
    }
  }
  std::cerr << std::endl;
}

template <class T> void debug(std::vector<std::vector<T>> &vv) {
  for (auto &v : vv) {
    print(v);
  }
}

inline bool inside(long long y, long long x, long long H, long long W) {
  return 0 <= y and y < H and 0 <= x and x < W;
}

template <class T> inline double euclidean_distance(T y1, T x1, T y2, T x2) {
  return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

template <class T> inline double manhattan_distance(T y1, T x1, T y2, T x2) {
  return abs(x1 - x2) + abs(y1 - y2);
}

template <typename T> T &chmin(T &a, const T &b) { return a = std::min(a, b); }

template <typename T> T &chmax(T &a, const T &b) { return a = std::max(a, b); }

template <class T> inline std::vector<T> unique(std::vector<T> v) {
  sort(v.begin(), v.end());
  v.erase(unique(v.begin(), v.end()), v.end());
  return v;
}

long long sum_of_arithmetic_progression(long long s, long long d, long long n) {
  return n * (2 * s + (n - 1) * d) / 2;
}

bool is_power_of_two(long long x) { return !(x & (x - 1)); }

long long gcd(long long a, long long b) {
  if (b == 0) {
    return a;
  }
  return gcd(b, a % b);
}

long long gcd(std::vector<long long> &v) {
  long long ans = v[0];
  for (int i = 1; i < (int)v.size(); ++i) {
    ans = gcd(ans, v[i]);
  }
  return ans;
}

long long lcm(long long a, long long b) {
  long long g = gcd(a, b);
  return a / g * b;
}

const int INF = 1u << 30u;
const long long LINF = 1ull << 58u;
const double EPS = 1e-9;
const long double PI = acos(-1.0);
const std::vector<int> dy2 = {0, 1}, dx2 = {1, 0};
const std::vector<int> dy4 = {0, 1, 0, -1}, dx4 = {1, 0, -1, 0};
const std::vector<int> dy8 = {0, -1, 0, 1, 1, -1, -1, 1},
                       dx8 = {1, 0, -1, 0, 1, 1, -1, -1};

using namespace std;

int main(int argc, char *argv[]) {
  cin.tie(0);
  ios::sync_with_stdio(false);

  string S;
  cin >> S;
  const int N = LEN(S);

  auto dp = make_v<int>(N + 1, 2020);
  dp[0][0] = 1;

  FOR(i, 0, N) {
    const int d = S[i] - '0';

    if (i != 0) {
      dp[i + 1][d % 2019] += 1;
    }

    FOR(j, 0, 2020) {
      if (dp[i][j] == 0) {
        continue;
      }

      dp[i + 1][(j * 10 + d) % 2019] += dp[i][j];
    }
  }

  LL ans = 0;
  FOR(i, 1, N + 1) { ans += dp[i][0]; }
  print(ans);

  return 0;
}