Problem p02579 (C++) — buggy submission, verdict: Time Limit Exceeded

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

typedef long long ll;
typedef pair<int, int> pii;
const int N = 1e3 + 5, mod = 1e9 + 7;

int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}}; // n - e - s - w
int h, w;                                           // height, width
int sh, sw;                                         // start
int eh, ew;                                         // end
int ans = -1;
int d[N][N];
char c[N][N];
bool m[N][N];

void bfs() {
  for (int i = 0; i < N; ++i) {
    for (int j = 0; j < N; ++j) {
      d[i][j] = mod;
    }
  }

  m[sh][sw] = true;
  d[sh][sw] = 0;

  deque<pii> q;
  q.push_front({sh, sw});

  while (q.size()) {
    pii cur = q.front();
    int curX = cur.first;
    int curY = cur.second;

    if (curX == eh && curY == ew) {
      ans = d[curX][curY];
      return;
    }

    q.pop_front();
    for (int i = 0; i < 4; ++i) {
      int x = curX + dir[i][0];
      int y = curY + dir[i][1];
      if (x < 1 || x > h || y < 1 || y > w) {
        continue;
      }

      if (c[x][y] == '#') {
        m[x][y] = true;
      }

      if (c[x][y] == '.' && (!m[x][y] || d[x][y] > d[curX][curY])) {
        m[x][y] = true;
        d[x][y] = d[curX][curY];
        q.push_front({x, y});
      }
    }

    for (int i = -2; i <= 2; ++i) {
      for (int j = -2; j <= 2; ++j) {
        if (i == 0 && j == 0) {
          continue;
        }

        int x = curX + i;
        int y = curY + j;
        if (x < 1 || x > h || y < 1 || y > w) {
          continue;
        }

        if (c[x][y] == '.' && !m[x][y]) {
          m[x][y] = true;
          d[x][y] = d[curX][curY] + 1;
          q.push_back({x, y});
        }
      }
    }
  }
  return;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  cin >> h >> w >> sh >> sw >> eh >> ew;

  for (int i = 1; i <= h; ++i) {
    for (int j = 1; j <= w; ++j) {
      cin >> c[i][j];
    }
  }

  bfs();
  cout << ans << endl;

  return 0;
}

Error: TLE

Fixed submission:

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

typedef long long ll;
typedef pair<int, int> pii;
const int N = 1e3 + 5, mod = 1e9 + 7;

int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}}; // n - e - s - w
int h, w;                                           // height, width
int sh, sw;                                         // start
int eh, ew;                                         // end
int ans = -1;
int d[N][N];
char c[N][N];
bool m[N][N];

void bfs() {
  for (int i = 0; i < N; ++i) {
    for (int j = 0; j < N; ++j) {
      d[i][j] = mod;
    }
  }

  m[sh][sw] = true;
  d[sh][sw] = 0;

  deque<pii> q;
  q.push_front({sh, sw});

  while (q.size()) {
    pii cur = q.front();
    int curX = cur.first;
    int curY = cur.second;

    if (curX == eh && curY == ew) {
      ans = d[curX][curY];
      return;
    }

    q.pop_front();
    for (int i = 0; i < 4; ++i) {
      int x = curX + dir[i][0];
      int y = curY + dir[i][1];
      if (x < 1 || x > h || y < 1 || y > w) {
        continue;
      }

      if (c[x][y] == '#') {
        m[x][y] = true;
      }
      if (c[x][y] == '.' && !m[x][y]) {
        m[x][y] = true;
        d[x][y] = d[curX][curY];
        q.push_front({x, y});
      }
    }

    for (int i = -2; i <= 2; ++i) {
      for (int j = -2; j <= 2; ++j) {
        if (i == 0 && j == 0) {
          continue;
        }

        int x = curX + i;
        int y = curY + j;
        if (x < 1 || x > h || y < 1 || y > w) {
          continue;
        }

        if (c[x][y] == '.' && !m[x][y]) {
          d[x][y] = d[curX][curY] + 1;
          q.push_back({x, y});
        }
      }
    }
  }
  return;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  cin >> h >> w >> sh >> sw >> eh >> ew;

  for (int i = 1; i <= h; ++i) {
    for (int j = 1; j <= w; ++j) {
      cin >> c[i][j];
    }
  }

  bfs();
  cout << ans << endl;

  return 0;
}