为啥50就爆内存了阿
import java.util.*;
class Main{
static int vis[][];
static char a[][];
static int n;
static int dx[]= {0,0,1,-1};
static int dy[]= {1,-1,0,0};
static int x2;
static int y2;

public static void main(String[] args) {
    Scanner in =new Scanner(System.in);
    n=in.nextInt();
    a=new char [n][n];
    int x=0;
    int y=0;
    for(int i=0;i<n;i++) {
        for(int j=0;j<n;j++) {
            String s=in.next();
            if(s.equals("A")) {
                x=i;
                y=j;
            }
            if(s.equals("B")) {
                x2=i;
                y2=j;
            }
            a[i][j]=s.charAt(0);
        }
    }
    vis=new int [n][n];
    bfs(x,y);
    if(ans==Integer.MAX_VALUE) {
        System.out.println(-1);
    }else {
        System.out.println(ans);
    }
}
static int ans=Integer.MAX_VALUE;
static class node{
    int x;
    int y;
    char t;
    int dist;
    public node(int x, int y, char t,int dist) {
        this.x = x;
        this.y = y;
        this.t = t;
        this.dist=dist;
    }

}
static void bfs(int x,int y) {
    Queue<node> q=new ArrayDeque<Main.node>();
    q.add(new node(x,y,'A',0));
    vis[0][0]=1;
    while(!q.isEmpty()) {
        node u=q.peek();
        q.poll();
        int x1=u.x;
        int y1=u.y;
        vis[x1][y1]=1;
        if(x1==x2&&y1==y2) {
            if(u.dist<ans) {
                ans=u.dist;
                return;
            }
        }
        for(int i=0;i<dx.length;i++) {
            int nx=x1+dx[i];
            int ny=y1+dy[i];
            if(nx>=0&&ny>=0&&nx<n&&ny<n&&vis[nx][ny]==0) {
                char t=u.t;
                if(t=='+') {
                    if(a[nx][ny]=='-'||a[nx][ny]=='B') {
                        q.add(new node(nx,ny,'-',u.dist+1));
                    }
                }else if(t=='-') {
                    if(a[nx][ny]=='+'||a[nx][ny]=='B') {
                        q.add(new node(nx,ny,'+',u.dist+1));
                    }
                }else if(t=='A'){
                        q.add(new node(nx,ny,a[nx][ny],u.dist+1));
                    }
            }
        }

    }
}

}