Problem p00541 (C++)

Buggy submission (status: Memory Limit Exceeded):
#include <bits/stdc++.h>
using namespace std;

#define st first
#define nd second
#define mp make_pair
#define space << " " <<
#define END << endl
#define pb push_back
#define fo(i, n) for (int i = 0; i < n; ++i)
#define ff(i, n) for (int i = 1; i < n; ++i)

typedef vector<int> vi;
typedef pair<int, int> pii;
typedef pair<int, pii> pi;
typedef long long ll;
typedef pair<int, ll> pil;
typedef pair<ll, int> pli;
typedef pair<ll, ll> pll;
typedef pair<ll, pll> pl;
typedef vector<pil> vil;

const int N = 4002;

int board[N][N], U[N][N], L[N][N], R[N][N], D[N][N];
int bit[N][2];
ll ans = 0;
int h, w, p, l;

void update(int u, int id, int val) {
  while (u < N) {
    bit[u][id] += val;
    u += (u & (-u));
  }
}
int get(int u, int id) {
  int ans = 0;
  while (u > 0) {
    ans += bit[u][id];
    u -= (u & (-u));
  }
  return ans;
}
void up(int id, int le, int ri) {
  if (le > ri)
    return;
  update(le, id, 1);
  update(ri + 1, id, -1);
}

void work(int x, int y) {
  vector<pair<int, pii>> a;
  fo(i, N) fo(j, 3) bit[i][j] = 0;
  while (x <= h && y <= w) {
    a.push_back(mp(min(L[x][y], U[x][y]), mp(1, x)));
    a.push_back(mp(min(R[x][y], D[x][y]), mp(0, x)));
    x++;
    y++;
  }
  sort(a.begin(), a.end());
  fo(i, a.size()) {
    pair<int, pii> u = a[i];
    if (u.nd.st == 1) {
      ans += 1LL * get(u.nd.nd, 1);
      up(0, u.nd.nd - u.st + 1, u.nd.nd - l + 1);
    } else {
      ans += 1LL * get(u.nd.nd, 0);
      up(1, u.nd.nd + l - 1, u.nd.nd + u.st - 1);
    }
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> h >> w >> l >> p;
  fo(i, p) {
    int u, v;
    cin >> u >> v;
    board[u][v] = 1;
  }
  ff(i, h + 1) ff(j, w + 1) {
    if (board[i][j]) {
      L[i][j] = U[i][j] = 0;
    } else {
      L[i][j] = L[i][j - 1] + 1;
      U[i][j] = U[i - 1][j] + 1;
    }
  }
  for (int i = h; i >= 1; --i)
    for (int j = w; j >= 1; --j) {
      if (board[i][j]) {
        R[i][j] = D[i][j] = 0;
      } else {
        R[i][j] = R[i][j + 1] + 1;
        D[i][j] = D[i + 1][j] + 1;
      }
    }
  ff(i, h + 1) work(i, 1);
  for (int j = 2; j <= w; ++j)
    work(1, j);
  cout << ans << endl;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define st first
#define nd second
#define mp make_pair
#define space << " " <<
#define END << endl
#define pb push_back
#define fo(i, n) for (int i = 0; i < n; ++i)
#define ff(i, n) for (int i = 1; i < n; ++i)

typedef vector<int> vi;
typedef pair<int, int> pii;
typedef pair<int, pii> pi;
typedef long long ll;
typedef pair<int, ll> pil;
typedef pair<ll, int> pli;
typedef pair<ll, ll> pll;
typedef pair<ll, pll> pl;
typedef vector<pil> vil;

const int N = 4002;

short board[N][N], U[N][N], L[N][N], R[N][N], D[N][N];
int bit[N][2];
ll ans = 0;
int h, w, p, l;

void update(int u, int id, int val) {
  while (u < N) {
    bit[u][id] += val;
    u += (u & (-u));
  }
}
int get(int u, int id) {
  int ans = 0;
  while (u > 0) {
    ans += bit[u][id];
    u -= (u & (-u));
  }
  return ans;
}
void up(int id, int le, int ri) {
  if (le > ri)
    return;
  update(le, id, 1);
  update(ri + 1, id, -1);
}

void work(int x, int y) {
  vector<pair<int, pii>> a;
  fo(i, N) fo(j, 3) bit[i][j] = 0;
  while (x <= h && y <= w) {
    a.push_back(mp(min(L[x][y], U[x][y]), mp(1, x)));
    a.push_back(mp(min(R[x][y], D[x][y]), mp(0, x)));
    x++;
    y++;
  }
  sort(a.begin(), a.end());
  fo(i, a.size()) {
    pair<int, pii> u = a[i];
    if (u.nd.st == 1) {
      ans += 1LL * get(u.nd.nd, 1);
      up(0, u.nd.nd - u.st + 1, u.nd.nd - l + 1);
    } else {
      ans += 1LL * get(u.nd.nd, 0);
      up(1, u.nd.nd + l - 1, u.nd.nd + u.st - 1);
    }
  }
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> h >> w >> l >> p;
  fo(i, p) {
    int u, v;
    cin >> u >> v;
    board[u][v] = 1;
  }
  ff(i, h + 1) ff(j, w + 1) {
    if (board[i][j]) {
      L[i][j] = U[i][j] = 0;
    } else {
      L[i][j] = L[i][j - 1] + 1;
      U[i][j] = U[i - 1][j] + 1;
    }
  }
  for (int i = h; i >= 1; --i)
    for (int j = w; j >= 1; --j) {
      if (board[i][j]) {
        R[i][j] = D[i][j] = 0;
      } else {
        R[i][j] = R[i][j + 1] + 1;
        D[i][j] = D[i + 1][j] + 1;
      }
    }
  ff(i, h + 1) work(i, 1);
  for (int j = 2; j <= w; ++j)
    work(1, j);
  cout << ans << endl;
}