Problem p00207 (C++)

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

using namespace std;

int w, h;
int gx, gy;
int vx[] = {0, 1, 0, -1};
int vy[] = {1, 0, -1, 0};
int block[100][100];
bool check[100][100];
bool flag;

void dfs(int y, int x) {

  /*
  for(int i = 0; i < h; ++i) {
    for(int j = 0; j < w; ++j) {
      if(i == y && j == x) cout << 'P';
      else if(i == gy && j == gx) cout << 'G';
      else cout << block[i][j];
    }
    cout << endl;
  }
  cout << endl;
  */

  if (y == gy && x == gx) {

    flag = true;
    return;

  } else {

    for (int i = 0; i < 4; ++i) {

      int ny = y + vy[i];
      int nx = x + vx[i];

      if (ny >= 0 && ny < h && nx >= 0 && nx < w && !check[ny][nx] &&
          block[ny][nx] && block[ny][nx] == block[y][x]) {

        check[ny][nx] = true;
        dfs(ny, nx);
        check[ny][nx] = false;
      }
    }
  }
}

int main() {

  int sx, sy;
  int n;
  int c, d, x, y;

  while (cin >> w >> h) {

    if (w == 0 && h == 0)
      break;

    cin >> sx >> sy;
    cin >> gx >> gy;
    cin >> n;

    --sx;
    --sy;
    --gx;
    --gy;

    for (int i = 0; i < h; ++i) {
      for (int j = 0; j < w; ++j) {
        block[i][j] = 0;
        check[i][j] = false;
      }
    }

    for (int i = 0; i < n; ++i) {

      cin >> c >> d >> x >> y;

      --x;
      --y;

      int bw, bh;

      if (d) {
        bw = 2;
        bh = 4;
      } else {
        bw = 4;
        bh = 2;
      }

      for (int j = 0; j < bh; ++j) {
        for (int k = 0; k < bw; ++k) {
          block[y + j][x + k] = c;
        }
      }
    }

    flag = false;
    check[sy][sx] = true;
    dfs(sy, sx);

    cout << (flag ? "OK" : "NG") << endl;
  }
}

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

using namespace std;

int w, h;
int gx, gy;
int vx[] = {0, 1, 0, -1};
int vy[] = {1, 0, -1, 0};
int block[100][100];
bool check[100][100];
bool flag;

void dfs(int y, int x) {

  /*
  for(int i = 0; i < h; ++i) {
    for(int j = 0; j < w; ++j) {
      if(i == y && j == x) cout << 'P';
      else if(i == gy && j == gx) cout << 'G';
      else cout << block[i][j];
    }
    cout << endl;
  }
  cout << endl;
  */

  if (y == gy && x == gx) {

    flag = true;
    return;

  } else {

    for (int i = 0; i < 4; ++i) {

      int ny = y + vy[i];
      int nx = x + vx[i];

      if (ny >= 0 && ny < h && nx >= 0 && nx < w && !check[ny][nx] &&
          block[ny][nx] && block[ny][nx] == block[y][x]) {

        check[ny][nx] = true;
        dfs(ny, nx);
        // check[ny][nx] = false;
      }
    }
  }
}

int main() {

  int sx, sy;
  int n;
  int c, d, x, y;

  while (cin >> w >> h) {

    if (w == 0 && h == 0)
      break;

    cin >> sx >> sy;
    cin >> gx >> gy;
    cin >> n;

    --sx;
    --sy;
    --gx;
    --gy;

    for (int i = 0; i < h; ++i) {
      for (int j = 0; j < w; ++j) {
        block[i][j] = 0;
        check[i][j] = false;
      }
    }

    for (int i = 0; i < n; ++i) {

      cin >> c >> d >> x >> y;

      --x;
      --y;

      int bw, bh;

      if (d) {
        bw = 2;
        bh = 4;
      } else {
        bw = 4;
        bh = 2;
      }

      for (int j = 0; j < bh; ++j) {
        for (int k = 0; k < bw; ++k) {
          block[y + j][x + k] = c;
        }
      }
    }

    flag = false;
    check[sy][sx] = true;
    dfs(sy, sx);

    cout << (flag ? "OK" : "NG") << endl;
  }
}