Problem p00454 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <cstring>
#include <iostream>
#include <queue>
#include <vector>
#define MAX_N 1000 + 16

using namespace std;

int N, H, W;
int X1[MAX_N], X2[MAX_N], Y1[MAX_N], Y2[MAX_N];
int fld[2 * MAX_N][2 * MAX_N], // ??????????????¨?????£??¨??????(i,
                               // j)??????????????????????????????
    dx[4] = {1, -1, 0, 0}, dy[4] = {0, 0, 1, -1};

// ????????????????°?????????????????????????????¬¬????§?????????????????????±???????§???????
int compress(int *x1, int *x2, int w) {
  vector<int> xs;

  for (int i = 0; i < N; ++i) {
    int tx1 = x1[i], tx2 = x2[i];
    if (1 <= tx1 && tx1 < w)
      xs.push_back(tx1);
    if (1 <= tx2 && tx2 < w)
      xs.push_back(tx2);
  }
  xs.push_back(0);
  xs.push_back(w);
  sort(xs.begin(), xs.end());
  xs.erase(unique(xs.begin(), xs.end()), xs.end());
  for (int i = 0; i < N; ++i) {
    x1[i] = find(xs.begin(), xs.end(), x1[i]) - xs.begin();
    x2[i] = find(xs.begin(), xs.end(), x2[i]) - xs.begin();
  }
  return xs.size() - 1;
}

int bfs() {
  int ans = 0;
  for (int i = 0; i < H; ++i) {
    for (int j = 0; j < W; ++j) {
      if (fld[i][j])
        continue;
      ++ans;
      queue<pair<int, int>> que;
      que.push(make_pair(j, i));
      while (!que.empty()) {
        int nx = que.front().first, ny = que.front().second;
        que.pop();

        for (int i = 0; i < 4; ++i) {
          int tx = nx + dx[i], ty = ny + dy[i];
          if (tx < 0 || W < tx || ty < 0 || H < ty || fld[ty][tx] > 0)
            continue;
          que.push(make_pair(tx, ty));
          fld[ty][tx] = 1;
        }
      }
    }
  }
  return ans;
}

///////////////////////////SubMain//////////////////////////////////
int main(int argc, char *argv[]) {
  while (cin >> W >> H, W | H) {
    cin >> N;
    for (int i = 0; i < N; ++i) {
      cin >> X1[i] >> Y1[i] >> X2[i] >> Y2[i];
    }

    memset(fld, 0, sizeof(fld));

    W = compress(X1, X2, W);
    H = compress(Y1, Y2, H);

    // imos-???
    for (int i = 0; i < N; i++) {
      fld[Y1[i]][X1[i]]++;
      fld[Y1[i]][X2[i]]--;
      fld[Y2[i]][X1[i]]--;
      fld[Y2[i]][X2[i]]++;
    }
    // ?¨?????´??§?
    for (int i = 0; i < H; i++) {
      for (int j = 1; j < W; j++) {
        fld[i][j] += fld[i][j - 1];
      }
    }
    // ???????´??§?
    for (int i = 1; i < H; i++) {
      for (int j = 0; j < W; j++) {
        fld[i][j] += fld[i - 1][j];
      }
    } // ?´??§??????????fld??????0??¨?????¨????????????
    cout << bfs() << endl;
  }
  return 0;
}
///////////////////////////End Sub//////////////////////////////////

Error: 0

Fixed submission:

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
using namespace std;

const int MAX_N = 1016;

int w, h, n;

int x1[MAX_N], x2[MAX_N], Y1[MAX_N], y2[MAX_N];

void solve();

int main() {
  // freopen("0531-input.txt", "r", stdin);
  while (~scanf("%d%d", &w, &h) && (w || h)) {
    scanf("%d", &n);
    for (int i = 0; i < n; ++i) {
      scanf("%d%d%d%d", x1 + i, Y1 + i, x2 + i, y2 + i);
    }
    solve();
  }
  return 0;
}

int compress(int *x1, int *x2, int w) {
  vector<int> xs;
  for (int i = 0; i < n; ++i) {
    xs.push_back(x1[i]);
    xs.push_back(x2[i]);
  }
  xs.push_back(0);
  xs.push_back(w);
  sort(xs.begin(), xs.end());
  xs.erase(unique(xs.begin(), xs.end()), xs.end());
  for (int i = 0; i < n; ++i) {
    x1[i] = find(xs.begin(), xs.end(), x1[i]) - xs.begin();
    x2[i] = find(xs.begin(), xs.end(), x2[i]) - xs.begin();
  }
  return xs.size() - 1;
}
int fld[MAX_N + 2][MAX_N + 2];
int dx[] = {0, 0, -1, 1};
int dy[] = {1, -1, 0, 0};
void solve() {
  memset(fld, 0, sizeof(fld));
  int W = compress(x1, x2, w);
  int H = compress(Y1, y2, h);
  for (int i = 0; i < n; ++i) {
    fld[Y1[i]][x1[i]]++;
    fld[y2[i]][x2[i]]++;
    fld[Y1[i]][x2[i]]--;
    fld[y2[i]][x1[i]]--;
  }
  // horizontal
  for (int y = 0; y < H; ++y) {
    for (int x = 1; x < W; ++x) {
      fld[y][x] += fld[y][x - 1];
    }
  }
  // vertical
  for (int x = 0; x < W; ++x) {
    for (int y = 1; y < H; ++y) {
      fld[y][x] += fld[y - 1][x];
    }
  }
  /*for (int y = H - 1; y >= 0; --y) {
      for (int x = 0; x < W; ++x) {
          printf("%d ", fld[y][x]);
      }
      printf("\\n");
  }*/
  int c = 0;
  for (int x = 0; x < W; ++x) {
    for (int y = 0; y < H; ++y) {
      if (fld[y][x])
        continue;
      queue<pair<int, int>> que;
      que.push(make_pair(y, x));
      fld[y][x] = 1;
      while (que.size()) {
        int xx = que.front().second, yy = que.front().first;
        que.pop();
        for (int i = 0; i < 5; ++i) {
          int nx = xx + dx[i], ny = yy + dy[i];
          if (nx < 0 || nx >= W || ny < 0 || ny >= H || fld[ny][nx])
            continue;
          fld[ny][nx] = 1;
          que.push(make_pair(ny, nx));
        }
      }
      ++c;
    }
  }
  printf("%d\\n", c);
}