Implement the "queue" data structure. Write a program that describes the queue and simulates the operation of the queue by implementing all the methods listed here. The program reads a sequence of commands and, depending on the command, performs one or another operation. After executing each command, the program should print one line. Possible commands for the program:
push n
Add the number n to the queue (the value of n is given after the command). The program should print ok.
pop
Remove the first element from the queue. The program should output its value.
front
The program should output the value of the first element without removing it from the queue.
size
The program should print the number of elements in the queue.
clear
The program should clear the queue and print ok.
exit
The program should print bye and exit.
Before executing the front and pop operations, the program must check whether the queue contains at least one element. If there is a front or pop operation in the input data, and the queue is empty, then the program should output the string error instead of a numeric value.
Input
Queue management commands are entered, one per line
Imprint
It is required to display the log of the queue operation, one message per line
Examples
| # |
Input |
Output |
| 1 |
push 1
exit |
ok
1
bye |
| 2 |
size
push 1
push 2
push 3
exit |
0
ok
1
ok
2
ok
3
bye |