一道关于停车计费的问题

#!/usr/bin/perl  
use strict;  
use warnings;  
use Data::Dumper;  
use Time::Local;  
use POSIX qw{strftime};  
my (%hash,%count)=();  
my $start_time = time;  
sub p_money{  #计算费用  
    my $time = shift;  
   return 5 if $time <= 600;  
   if ($time>600 and $time<1800){  
    my $min;  
     $time%60==0?$min = ($time-600)/60:$min= int( ($time-600)/60 +1);  
        my $mon_minute = 5+$min*5;  
       return $mon_minute;  
   }  
}  
my (@arr,$end_time);  
while(1){  
    my ($start);  
   $end_time=time;  
print  "Car Number :";  
   eval{  
local $SIG{ALRM}=sub {die "timeout\n";};  
  alarm(5);  
    chomp( $start = <>);        #此处设施中断  5秒内没有用户输入就继续循环，  
    push @{$hash{$start}},time;  
    $count{$start}++ if defined $start;  
    alarm(0);  
   };  
if ($end_time-$start_time>20){   #这里程序运行20秒，则退出循环，打印车辆的费用  
        for (sort keys %hash){  
my $stop_time = time()-$hash{$_}[0];  
        my $car_start_time = strftime("%Y-%m-%d %H:%M:%S", localtime($hash{$_}[0]));  
        my $car_stop_time = strftime("%Y-%m-%d %H:%M:%S", localtime(time));  
        push @arr,"$_\t$car_start_time $car_stop_time $stop_time\t200\n";  
        }  
   print "\n车号\t开始时间\t离开时间\t停车时间\t价格\n";  
   print @arr;  
        exit;  
    }  
   if(defined $start  and  ($count{$start}||0) >1 ){  
        push @{$hash{$start}},time;  
        my $stop_time = $hash{$start}[-1]-$hash{$start}[0];  
        my $car_money = p_money $stop_time;  
        my $car_start_time = strftime("%Y-%m-%d %H:%M:%S", localtime($hash{$start}[0]));  
        my $car_stop_time = strftime("%Y-%m-%d %H:%M:%S", localtime($hash{$start}[-1]));  
        push @arr, "$start\t$car_start_time $car_stop_time $stop_time\t$car_money\n";  
        delete $count{$start}; #删除 出库车辆  
        delete $hash{$start};  
        redo;  #继续等待用户输入  
    }else{  
        redo;  
    }  
}