北大poj- 1028

Web Navigation

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 33281		Accepted: 14836

Description

Standard web browsers contain features to move backward and forward among the pages recently visited. One way to implement these features is to use two stacks to keep track of the pages that can be reached by moving backward and forward. In this problem, you are asked to implement this.
The following commands need to be supported:

BACK: Push the current page on the top of the forward stack. Pop the
page from the top of the backward stack, making it the new current
page. If the backward stack is empty, the command is ignored.

FORWARD: Push the current page on the top of the backward stack. Pop
the page from the top of the forward stack, making it the new current
page. If the forward stack is empty, the command is ignored.

VISIT : Push the current page on the top of the backward stack,
and make the URL specified the new current page. The forward stack is
emptied.

QUIT: Quit the browser.

Assume that the browser initially loads the web page at the URL http://www.acm.org/

Input

Input
is a sequence of commands. The command keywords BACK, FORWARD, VISIT,
and QUIT are all in uppercase. URLs have no whitespace and have at most
70 characters. You may assume that no problem instance requires more
than 100 elements in each stack at any time. The end of input is
indicated by the QUIT command.

Output

For
each command other than QUIT, print the URL of the current page after
the command is executed if the command is not ignored. Otherwise, print
"Ignored". The output for each command should be printed on its own
line. No output is produced for the QUIT command.

Sample Input

VISIT http://acm.ashland.edu/
VISIT http://acm.baylor.edu/acmicpc/
BACK
BACK
BACK
FORWARD
VISIT http://www.ibm.com/
BACK
BACK
FORWARD
FORWARD
FORWARD
QUIT

Sample Output

http://acm.ashland.edu/
http://acm.baylor.edu/acmicpc/
http://acm.ashland.edu/
http://www.acm.org/
Ignored
http://acm.ashland.edu/
http://www.ibm.com/
http://acm.ashland.edu/
http://www.acm.org/
http://acm.ashland.edu/
http://www.ibm.com/
Ignored

Source

East Central North America 2001

 

分析： 水题，题目怎么说就怎么做。

 

 #include <stdio.h>
 #include <string.h>

 #define MAX_NUM 100

 int main()
 {
     char input[MAX_NUM];
     char now[MAX_NUM] = "http://www.acm.org/";
     char stackForward[MAX_NUM][MAX_NUM];
     char stackBack[MAX_NUM][MAX_NUM];
     int stackF = ;
     int stackB = ;

     memset(stackForward, , MAX_NUM * MAX_NUM * sizeof(char));
     memset(stackBack, , MAX_NUM * MAX_NUM * sizeof(char));

     while()
     {
         scanf(" %s",input);
         if(strcmp(input, "VISIT") == )
         {
             stackF = ;
             strcpy(stackBack[stackB++], now);
             scanf(" %s", now);
         }
         else if(strcmp(input, "BACK") == )
         {
             if(stackB == )
             {
                 printf("Ignored\n");
                 continue;
             }
             strcpy(stackForward[stackF++], now);
             strcpy(now, stackBack[--stackB]);
         }
         else if(strcmp(input, "FORWARD") == )
         {
             if(stackF == )
             {
                 printf("Ignored\n");
                 continue;
             }
             strcpy(stackBack[stackB++], now);
             strcpy(now, stackForward[--stackF]);
         }
         else if(strcmp(input, "QUIT") == )
         {
             break;
         }
         printf("%s\n", now);
     }

     return ;
 }