题目链接：

思路：先合并，然后判断根结点是否唯一，如果是，则在判断是否是欧拉路；否则，直接结束。

1 #include
      
        2 #include
       
         3 #include
        
          4 using namespace std; 5 const int MAXN=100000+10; 6 int In[MAXN],Out[MAXN]; 7 int parent[MAXN]; 8 bool mark[MAXN]; 9 int n;10 11 12 void Initiate(){13     for(int i=0;i
         
          =0;s=parent[s]);21     while(s!=x){22         int tmp=parent[x];23         parent[x]=s;24         x=tmp;25     }26     return s;27 }28 29 void Union(int R1,int R2){30     int r1=Find(R1);31     int r2=Find(R2);32     if(r1!=r2){33         parent[r1]=r2;34     }35 }36 37 int main(){38     int _case;39     scanf("%d",&_case);40     while(_case--){41         scanf("%d",&n);42         Initiate();43         memset(mark,false,sizeof(mark));44         memset(In,0,sizeof(In));45         memset(Out,0,sizeof(Out));46         for(int i=0;i
          
           1){63             printf("The door cannot be opened.\n");64         }else {65             int p[27];66             int k=0;67             for(int i=0;i<26;i++){68                 if(mark[i]&&In[i]!=Out[i]){69                     p[k++]=i;70                 }71             }72             if(k==0){73                 printf("Ordering is possible.\n");74             }else {75                 if(k==2&&abs(In[p[0]]-Out[p[0]])==1&&abs(In[p[1]]-Out[p[1]])==1){76                     printf("Ordering is possible.\n");77                 }else 78                     printf("The door cannot be opened.\n");79             }80         }81     }82     return 0;83 }