const int dr[4] = {1, -1, 0, 0};
const int dc[4] = {0, 0, 1, -1};

int bfs_grid(int sr, int sc, int tr, int tc,
             const vector<string> &grid) {
    int n = grid.size m = grid[0].size();
    vector<vector<int>> dist(n, vector<int>(m, -1));
    queue<pair<int, int>> q;
    dist[sr][sc] = 0;
    q.push({sr, sc});
    while (!q.empty()) {
        auto [r, c] = q.front();
        q.pop();
        if (r == tr && c == tc) {
            return dist[r][c];
        }
        for (int k = 0; k < 4; ++k) {
            int nr = r + dr[k], nc = c + dc[k];
            if (nr < 0 || nr >= n || nc < 0 || nc >= m) continue;
            if (grid[nr][nc] == '#') continue;
            if (dist[nr][nc] != -1) continue;
            dist[nr][nc] = dist[r][c] + 1;
            q.push({nr, nc});
        }
    }
    return -1;
}