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imbored

Sat Jan 02, 2010 7:47 pm


Deleting in Linked List

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What is it you are trying to achieve?
Having a procedure delete a value from the linked list... also make it a circular linked list.


What is the problem you are having?
I understand the box things 
Describe what you have tried to solve this problem
i tried replacing the value that needs to be deleted with the next value and it keeps going untill the end.. but it didnt end up great either i programmed it wrong or its just wrong... i started from scratch from what i had before.

Post any relevant code (You may choose to attach the file instead of posting the code if it is too long)
 this is what i got.. it saves the inputs into the linked list and outputs it. it is choppy and inefficient... but i dont really know how to make it more efficient. but first thing is first how to make it delete o.o''


var PointerType : collection of
    record
        Data : string (40)
        Next : pointer to PointerType
        Prev : pointer to PointerType
    end record
var Backup : collection of
    record
        Data : string (40)
        Next : pointer to Backup
        Prev : pointer to Backup
    end record
%------------------- procedure---------------------------------------

procedure First (var InsertRecord, ListStart, ListEnd : pointer to PointerType, spNames : string)
    new InsertRecord
    ListEnd := InsertRecord
    ^InsertRecord.Next := nil
    ^InsertRecord.Data := spNames
    ListStart := InsertRecord
end First
procedure bFirst (var bIRecord, bListStart, bListEnd : pointer to Backup, spNames : string)
    new bIRecord
    bListEnd := bIRecord
    ^bIRecord.Next := nil
    ^bIRecord.Data := spNames
    bListStart := bIRecord
end bFirst
procedure InName (var InsertRecord, ListStart, ListEnd : pointer to PointerType, spName : string, var ipAm : int)
    new InsertRecord
    ^InsertRecord.Next := ListStart
    ^ListStart.Prev := InsertRecord
    ^InsertRecord.Data := spName
    ListStart := InsertRecord
    ipAm += 1
end InName
procedure bInName (var bIRecord, bListStart, bListEnd : pointer to Backup, spName : string)
    new bIRecord
    ^bIRecord.Next := bListStart
    ^bListStart.Prev := bIRecord
    ^bIRecord.Data := spName
    bListStart := bIRecord
end bInName
procedure Circular (var InsertRecord, ListStart, ListEnd : pointer to PointerType)
    InsertRecord := ListEnd
end Circular
procedure OutName (ListEnd : pointer to PointerType, ipAm : int)
    var i : int := 0
    var TempList := ListEnd
    loop
        i += 1
        put ^TempList.Data
        exit when i = ipAm
        TempList := ^TempList.Prev
    end loop
end OutName
procedure bOutName (bListEnd : pointer to Backup, ipAm : int)
    var i : int := 0
    var TempList := bListEnd
    loop
        i += 1
        put ^TempList.Data
        exit when i = ipAm
        TempList := ^TempList.Prev
    end loop
end bOutName
%----------------------- main----------------------------------------
var InsertRecord, ListStart, ListEnd : pointer to PointerType
var bIRecord, bListStart, bListEnd : pointer to Backup
var sNames : string
var iAm : int := 1
var iAm2 : int := 1
put "Input the name of a contestant"
get sNames : *
First (InsertRecord, ListStart, ListEnd, sNames)
bFirst (bIRecord, bListStart, bListEnd, sNames)
if (sNames = 'Fin') or (sNames = 'fin') then
    %nothing
else
    loop
        put "Input the name of a contestant"
        get sNames : *
        exit when (sNames = 'fin') or (sNames = 'Fin')
        InName (InsertRecord, ListStart, ListEnd, sNames, iAm)
        bInName (bIRecord, bListStart, bListEnd, sNames)
    end loop
end if
Circular (InsertRecord, ListStart, ListEnd)
cls
iAm2 := iAm
put "List: "
OutName (ListEnd, iAm)
put "Which Contestant do you want to elliminate?"
get sNames
%delete
put "Backup : "
bOutName (bListEnd, iAm2)
put "Remaining: "
OutName(ListEnd, iAm)



Please specify what version of Turing you are using
4.1.1


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[Gandalf]

Sun Jan 03, 2010 2:10 pm


RE:Deleting in Linked List

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Well first thing's first, have you investigated this problem yourself?  Linked lists are very common, and there are plenty of resources on just about anything to do with them.

Here's a quick link from Google which might help on delete: http://www.cs.bu.edu/teaching/cs112/spring-2000/linked-list-delete/

This is a great way to learn/practice recursion, so try to follow that route.  Just go slowly, case-by-case, and ensure that each piece of code you write is accurate.


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imbored

Sun Jan 03, 2010 3:31 pm


RE:Deleting in Linked List

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yea i saw that before but i dont know how to program it... i dont get the C++ codes


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[Gandalf]

Sun Jan 03, 2010 4:33 pm


RE:Deleting in Linked List

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Perhaps try the following site instead, particularly the "modifying lists" section.  It may even "convert" you to Python, given that Turing is a very ugly language in which to write linked lists. :)

http://ada.rg16.asn-wien.ac.at/~python/how2think/english/chap17.htm

Try to generalize what they do for the 2nd element of a linked list to an arbitrary element.  I'm sure you can find something to clarify the concept.  If you have any specific questions, you can then post them here.


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imbored

Sun Jan 03, 2010 4:49 pm


RE:Deleting in Linked List

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this site is better but reguarding the converting... i can't do that. This is part of an assignment. i was suppose to use pascal but it wasn't working on my computer so i used turing which is already on my computer. Though this site looks alot more helpful i really dont fully understand it. I dont understand how to shift the pointer because i dont fully understand the functions regarding the pointer.

edit : okay nvm.. i read it a few times... and i dont get it lol.