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puzzling linked lists

Posted on 1997-04-04
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Last Modified: 2010-04-15
here is a problem given to me by one of my friends.i have racked my brains but am unable to solve it.
  Given a pointer to the head of a singly linked list, reverse the order of the list and return a pointer to the new head?
 please provide me the solution ASAP i am very inquisitive
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Question by:latha
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3 Comments
 

Accepted Solution

by:
aleroy earned 100 total points
ID: 1249811
Here is a little program that does the thing
It use C++ syntax but should work on a C compiler without big change.

#include <stdio.h>
 
struct list {
  int one;
  list *next;
};
 
void print(list *l)
{
list *ll=l;
while (ll!=NULL)
{
  printf("%i ",ll->one);
  ll=ll->next;
}
printf("\n");
}

main()
{
list *l=NULL;
list *ll, *lll;;
int x;
scanf("%i ",&x);
while (x!=0)
{
  ll=l;
  l=new list;
  l->one=x;
  l->next=ll;
  scanf("%i",&x);
}
print(l);
 
//Here is the stuff
ll=NULL;
if (l!=NULL) lll=l->next;
while (l!=NULL)
{
  l->next=ll;
  ll=l;
  l=lll;
  if (lll!=NULL) lll=l->next;
}
l=ll;
//End of the stuff
 
print(l);
}

The whole thing stand on the use of 3 pointers :
the main pointer that follow the list
a pointer to the previous element
a pointer to the next element;

Given that, the problem is very simple.


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Expert Comment

by:sanjiv040897
ID: 1249813
To latha : My code could in fact be more clear with some comment.

To sanjiv : Very funny.
You have missed the case of a empty list.
And also something worst : out of your code :
while (pCurrentNode != NULL)
{
...//The content doesn't matter
}
return pCurrentNode ;
}
I THINK pCurrentNode COULD BE EQUAL to NULL WHEN RETURNED.


In my code, change :
l   to pCurrentNode
ll  to pPrevNode
lll to pNextNode
My code has been compiled and tested.

0
 

Expert Comment

by:aleroy
ID: 1249814
Dear aleroy,

I completely agree with u about the problems u have pointed out.  I did not compile and test the program,  I don't have time to do that.  My intention was to give a quick start to latha and not to spoon-feed the solution.  I hope latha knows enough C programming to fix such problems.  


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