假设某银行有4个窗口对外接待客户,从早晨银行开门起不断有客户进入银行。由于每个窗口在某个时刻只能接待一个客户，因此在客户人数众多时需要在每个窗口前顺次排队，对于刚进入银行的客户，如果某个窗口的业务员正空闲，则可上前输业务；反之，若4个窗口均有客户所占，他便会排在人数最少的队伍后面。编制一个程序模拟银行的这种业务活动并计算一天中客户在银行的平均逗留时间。-Assuming a bank has four reception window external customers, from the morning bank customer has ever opened the door to enter the bank. Since each window at a certain time only to receive a client, and therefore need a large number of customers in each window before the sequential queue, for just entering the bank