void bfs(int sx,int sy,int ex,int ey){
queue<Node>q;
memset(dis,-1,sizeof dis);
q.push({sx,sy});
dis[sx][sy] = 0;
while (!q.empty()){
Node now=q.front();
q.pop();
if(now.xex&& now.yey) break;
for(int i=0;i<4;i++){
int nx=now.x+dx[i];
int ny=now.y+dy[i];
if(nx>=1&&nx<=n&&ny>=1&&ny<=m&&g[nx][ny]==0
&& dis[nx][ny]==-1){
dis[nx][ny]=dis[now.x][now.y]+1;
q.push({nx,ny});
}
}
}
}