Question

i have wrote code for quicksort with linked list ,here is code

#include<stdio.h>
#include<iostream>
using namespace std;
typedef struct _tagIntegerList
{
    int  nInteger;
    struct _tagIntegerList *prev;
    struct _tagIntegerList *next;


}IntegerList;
IntegerList *firstitem=NULL;
IntegerList *lastitem=NULL;
void addlist(int n)
{

IntegerList *pitem=new IntegerList;
pitem->nInteger=n;
if ( firstitem==NULL){
firstitem=lastitem=pitem;
pitem->next=pitem->prev=NULL;

}
else{
    lastitem->next=pitem;
    pitem->prev=lastitem;
    lastitem=pitem;
    pitem->next=NULL;


}




}
void removeall(){
    IntegerList *delitem,*pitem=firstitem;
    while(pitem!=NULL){
        delitem=pitem;
        pitem=pitem->next;
        delete delitem;



    }

    firstitem=lastitem=NULL;
}


void print(){

    IntegerList * pitem=firstitem;
    while(pitem!=NULL){

        cout<<pitem->nInteger<<" ";
        pitem=pitem->next;


    }

}
// Quick Sort List
void quicksort(IntegerList *left, IntegerList *right)
{
    IntegerList *start;
    IntegerList *current;
    int copyinteger;

    if (left==right) return ;
    start=left;
    current=start->next;
    while(1){
        if (start->nInteger<current->nInteger){
            copyinteger=current->nInteger;
            current->nInteger=start->nInteger;
        start->nInteger=copyinteger;


        }
// Check if we have reached the right end
        if (current=right) break;
        current=current->next;






    }



    //swap first and current items
    copyinteger=left->nInteger;
    left->nInteger=current->nInteger;
    current->nInteger=copyinteger;
        IntegerList *oldcurrent=current;
        // Check if we need to sort the left hand size of the Current point
        current=current->prev;
        if (current!=NULL){
            if ((left->prev!=current)&& (current->next!=left))
                quicksort(left,current);
                }
current=oldcurrent;
current=current->next;
if (current!=NULL){

    if ((current->prev!=right)&& (right->next!=current))
        quicksort(current,right);

}
}
int main(){
    addlist(100);
    addlist(12);
    addlist(56);
    addlist(67);
    addlist(4);
    addlist(91);
    addlist(34);
    addlist(59);
    addlist(42);
    addlist(20);
    addlist(83);
    addlist(74);
    addlist(33);
    addlist(79);
    addlist(49);
    addlist(51);

    quicksort(firstitem,lastitem);
    print();
    removeall();
 return 0;
}

but output is not what i am expecting,here is result

4 56 67 12 91 34 59 42 20 83 74 33 79 49 51 100 

please help me what is wrong with this code?and also i am interested complexity of algorithm is it same O(nlogn)?

Answer 1

I assume current=right should be current==right
in if (current=right) break;