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'InsertionSort'ing a linked list

Posted on 1998-10-23
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Last Modified: 2011-09-20
Does anyone have code for Sorting a linked list using InsertionSort? Sorting by file size, date/time and then if necessary ID.  Without allocating any additional memory.  URGENT.  Bonus: if you determine the theoretical runtime.
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Question by:stuckart
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by:kellyjj
ID: 1253772
sounds like homework to  me. You should try this yourself and then  ask on the parts you are having probs with.
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Author Comment

by:stuckart
ID: 1253773
This is not a homework question.  I am trying to teach myself.  It is easiest for me to learn by example.  The part that is hardest for me is the swapping of the pointers.
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by:ozo
ID: 1253774
what have you tried?
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Author Comment

by:stuckart
ID: 1253775
Have in mind that I don't quite understand pointers that well.

void InsertionSort (Node *pHead)
  {
    Node *pCur = *pHead, *pTemp = *pHead;
    while( pCur)      <------   don't know what to put here, want to check if pCur is valid
      {
         pCur  =  pCur->pNext;
         while( pTemp->value > pCur->value)
            {
              swap them here.  Not sure how to move the pointers to do this.
            }
      }
}

In my Data structure I have   File, Date, ID  they are incremented by 1.
I'll put the exact code here, once my e-mail provider gets back online.  Figures huh.

thanks,
Jerry

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Accepted Solution

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rwilson032697 earned 100 total points
ID: 1253776
Your code is pretty much there. The while (pCur) is fine as long as pCur is set to NULL when it runs into the end of the list.

Instead of the inner while do this for the insertion:

        if( pTemp->value > pCur->value)
        {
           pTemp->nNext = pCur->pNext;
           pCur->pNext = pTemp;
        }

In terms of theoretical runtime this will be O(n squared). If you had used an array it would have been O(n log n).

To swap two pointers do this:

Node *SwapTemp = SecondNode;
SecondNode = FirstNode;
FirstNode = SwapTemp;

Cheers,

Raymond.
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Expert Comment

by:rwilson032697
ID: 1253777
Just a wee note: The O(n log n) for an array assumes you use a binary search to locate the insertion positon - the overhead of the actual array insertion operation is ignored.
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Author Comment

by:stuckart
ID: 1253778
Thank you very much.  I actually had it almost exactly like you said, but I didn't have the *'s in the right place.  Thank you again,

Jerry Stuckart
stuckart@csd.uwm.edu

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