题意：问两个迷宫是否存在公共最短路。

题解：两个反向bfs建立层次图，一遍正向bfs寻找公共最短路

#include
     
      #include
      
       #include
       
        using namespace std;const int maxn = 500+1;int d1[maxn][maxn];int d2[maxn][maxn];char g1[maxn][maxn];char g2[maxn][maxn];int n,m;struct node{    int x,y;    node(int X = 0, int Y = 0){        x = X; y = Y;    }};int dx[] = {
   1,-1,0,0};int dy[] = {
   0,0,1,-1};//1,1void rbfs(int id){    char (*G)[maxn];    int (*vis)[maxn];    if(id == 1) G = g1, vis = d1;    else G = g2, vis = d2;    memset(vis,-1,sizeof(d1));    queue
        
         q;    node u(n-1,m-1);    q.push(u);    vis[u.x][u.y] = 0;    while(q.size()){        u = q.front();q.pop();        if(u.x == 0 && u.y == 0) return;        for(int i = 0; i < 4; i++){            int nx = u.x + dx[i], ny = u.y + dy[i];            if(nx>=0&&nx
         
          =0&&ny
          
           q; q.push(node(0,0)); int tx = n-1, ty = m-1; while(q.size()){ node &u = q.front(); if(u.x == tx && u.y == ty) return true; for(int i = 0; i < 4; i++){ int nx = u.x + dx[i], ny = u.y + dy[i]; if(nx>=0&&nx
           
            =0&&ny