【ACM模式】队列操作

求解代码

publicstaticvoidmain(String[]args)throwsIOException{BufferedReaderbr=newBufferedReader(newInputStreamReader(System.in));StreamTokenizerin=newStreamTokenizer(br);PrintWriterout=newPrintWriter(newOutputStreamWriter(System.out));Deque<Integer>queue=newArrayDeque<>();while(in.nextToken()!=StreamTokenizer.TT_EOF){intn=(int)in.nval;for(inti=0;i<n;i++){in.nextToken();inta=(int)in.nval;switch(a){case1:in.nextToken();queue.add((int)in.nval);break;case2:if(queue.isEmpty()){out.println("ERR_CANNOT_POP");}else{queue.pollFirst();}break;case3:if(queue.isEmpty()){out.println("ERR_CANNOT_QUERY");}else{out.println(queue.peekFirst());}break;case4:out.println(queue.size());break;default:break;}}}out.flush();out.close();}