queue

代码说明：

  队列是一种特殊的线性表，是一种先进先出(FIFO)的数据结构。它只允许在表的前端(front)进行删除操作，而在表的后端(rear)进行插入操作。(Queue is a special kind of linear table, is a first in first out (FIFO) data structure. It is only allowed in the front of the table (front) to delete, and at the rear end of table insert (rear).)