BFS板子题

#include <iostream>
#include <string>
#include <queue>
using namespace std;
int n, m;
string maze[110];
bool vis[110][110];
int dir[4][2] = { {-1, 0}, {0, -1}, {1, 0}, {0, 1} };
bool in(int x, int y)
{
    return 0 <= x && x < n && 0 <= y && y < m;
}
struct node
{
  int x,y,d;
    node (int xx, int yy,int dd)
    {
        x = xx;
        y = yy;
        d = dd;
    }
};
int bfs(int sx, int sy)
{
    queue<node> q;
    q.push(node(sx,sy,0));
    vis[sx][sy] = true;
    while (!q.empty())
    {
        node now = q.front();
        q.pop();
        for(int i = 0; i < 4; i++)
        {
            int tx = now.x + dir[i][0];
            int ty = now.y + dir[i][1];
            if (in(tx,ty) && maze[tx][ty] != '*' && !vis[tx][ty])
            {
                if (maze[tx][ty] == 'T')
                {
                    return now.d + 1;
                }
                else
                {
                    vis [tx][ty] = true;
                    q.push(node(tx,ty,now.d + 1));
                }
            }
        }
    }
    return -1;
}
int main()
{
    cin >> n >> m;
    for (int i = 0; i < n; i++)
    {
        cin >> maze[i];
    }
    int x, y;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < m; j++)
        {
            if (maze[i][j] == 'S')
            {
                x = i, y = j;
            }
        }
    }
    cout << bfs(x,y) << endl;
    return 0;
}