> 一下是代码：
> #include <iostream>
> using namespace std;
> int main()
> {
> 	int n;
> 	int i,j,k;
> 	int a[1005],pre[1005];
> 	int stack[1005];
> 	for(i=1;i<=1000;i++)
> 		 pre[i]=i;
>      	cin>>n;
> 	  while( n!=0)
> 	  {
> 		  while(cin>>a[1])
> 		  {
> 			  if(a[1]==0)  break ;
> 		  for(i=2;i<=n;i++)
> 			  cin>>a[i];
>           i=j=k=1;
> 		  while(j<=n &&i<=n)
> 		  {
> 			  if(a[i]==pre[j])
> 			  {  
> 				  i++;j++; 
> 				  continue;
> 			  }
> 			  if(k>1)	 { if(a[i]==stack[k-1])  { i++; k--; continue;}}
> 					stack[k]=pre[j];
> 			    	 k++;j++;
> 		  }
> 	   if(i<=n )  
> 	   {
> 		   for(j=i;j<=n;j++)
> 			   if(a[j]==stack[k-1]) k--;
> 			      else break;
> 	   }
> 		if(j>n) cout<<"Yes"<<endl;
> 		  else cout<<"No"<<endl;
> 	  }
> 		  cin>>n;
> 		  if(n!=0)
> 		    cout<<endl; 
> 	  }
> 	return 0;
> }