HDOJ1195 双向BFS //单向也可以过 没想清

 #include<cstdio>
 #include<map>
 #include<vector>
 #include<stack>
 #include<iostream>
 #include<algorithm>
 #include<cstring>
 #include<cmath>
 #include<queue>
 #include<cstdlib>
 #define PI acos(-1.0)
 using namespace std;
 typedef long long ll;
 const ll mood=1e9+;
 const double eps=1e-;
 const int N=1e4+;
 const int MAXN=;
 struct node{
     string password;
     int cnt;
     }now,tmp;
 string beg,end;
 map<string,int>back_vis;
 map<string,int>vis;
 queue<struct node>q;
 queue<struct node>back_q;
 int back_bfs(int n)//反向BFS，每次只搜一层,即第n层
 {
     while(back_q.front().cnt<=n)
     {
         now=back_q.front();
         back_q.pop();
         for(int i=;i<;i++)
         {   //各个位-1\
                tmp=now;
             if(tmp.password[i]!='')
                 tmp.password[i]--;
             else   tmp.password[i]='';
             if(vis.find(tmp.password)!=vis.end())//判断是否在正向队列中找到
             return tmp.cnt++vis[tmp.password];
             if(back_vis.find(tmp.password)==back_vis.end())
             {
                 tmp.cnt++;
                 back_q.push(tmp);
                 back_vis[tmp.password]=tmp.cnt;
             }   //各个位+1
             tmp=now;
             if(tmp.password[i]!='')   tmp.password[i]++;
             else   tmp.password[i]='';
             if(vis.find(tmp.password)!=vis.end())//判断是否在正向队列中找到
                 return tmp.cnt++vis[tmp.password];
             if(back_vis.find(tmp.password)==back_vis.end())
             {
                 tmp.cnt++;
                 back_q.push(tmp);
                 back_vis[tmp.password]=tmp.cnt;
             }
         }
         for(int i=;i<;i++)
         {
             tmp=now;
             swap(tmp.password[i],tmp.password[i+]);
             if(vis.find(tmp.password)!=vis.end())//判断是否在正向队列中找到   、
             return tmp.cnt++vis[tmp.password];
             if(back_vis.find(tmp.password)==back_vis.end())
             {   tmp.cnt++;   back_q.push(tmp);   back_vis[tmp.password]=tmp.cnt;   }
         }
     }
     return -;
 }
 int bfs()
 {
     while(!q.empty())
         q.pop();//清空正向BFS的队列
     now.password=beg;
     now.cnt=;
     q.push(now);
     vis[beg]=;
     while(!q.empty())
     {
         int n=q.front().cnt;
         while(q.front().cnt<=n)
         {
             now=q.front();   q.pop();
             for(int i=;i<;i++)
             {   //各个位-1
                 tmp=now;
                 if(tmp.password[i]!='')
                        tmp.password[i]--;
                 else   tmp.password[i]='';
                 if(back_vis.find(tmp.password)!=back_vis.end())//判断是否在反向队列中找到
                 return tmp.cnt++back_vis[tmp.password];
                 if(vis.find(tmp.password)==vis.end())
                 {   tmp.cnt++;   q.push(tmp);   vis[tmp.password]=tmp.cnt;   }   //各个位+1
                 tmp=now;
                 if(tmp.password[i]!='')   tmp.password[i]++;
                 else   tmp.password[i]='';
                 if(back_vis.find(tmp.password)!=back_vis.end())//判断是否在反向队列中找到
                 return tmp.cnt++back_vis[tmp.password];
                 if(vis.find(tmp.password)==vis.end())
                 {   tmp.cnt++;   q.push(tmp);   vis[tmp.password]=tmp.cnt;   }
             }
             for(int i=;i<;i++)
             {
                 tmp=now;
                 swap(tmp.password[i],tmp.password[i+]);
                 if(back_vis.find(tmp.password)!=back_vis.end())//判断是否在反向队列中找到
                 return tmp.cnt++back_vis[tmp.password];
                 if(vis.find(tmp.password)==vis.end())   {
                     tmp.cnt++;   q.push(tmp);
                     vis[tmp.password]=tmp.cnt;
                 }
             }
         }
         int ret=back_bfs(now.cnt);
         if(ret!=-)
             return ret;
     }
 }
 int main(){
     int t;
     while(cin>>t)
     {
         while(t--)
         {
             cin>>beg;
             cin>>end;
             vis.clear();//清空map
             back_vis.clear();//清空map
             while(!back_q.empty())
             back_q.pop();//清空反向BFS的队列
             now.password=end;
             now.cnt=;
             back_q.push(now);
             back_vis[end]=;//将反向BFS的起始点入队列标记
             int ret=bfs();
             cout<<ret<<endl;
         }
     }
     return ;
 }    

还没懂