Quick Sort In Data Structure

   ⇰   QUICK SORT :-

Quick sort is one of the type of sorting technique. It follows the divide and conquer algorithm. The Quick sort treats an array as a list of elements. When sorting process begins, it selects the List's middle element as the list pivote. The algorithm then divides the list into two sub-lists, one with the elements that are less then the list pivote and other list with elements greater then or equal to list pivote. 

 The algorithm then recursively invokes or calls itself with both the list. Each time when the sorting algorithm is invoked, it further divides the elements into smaller sub-lists. This algorithm is quite efficient for large-sized data. In quick Sort generally middle element of list is considered as pivote, but we can  take pivot in different ways as follows:- 

  i > picking first element as pivot.

 ii > picking last element as pivot

iii > Pick a random element as pivot.

iv > Pick middle element as pivot (We are using it in example).

EXAMPLE :-

Let us take a unsorted list :-

          8 11 13 9 52 44 77 66 12

  ⇰  ALGORITHM OF QUICK SORT :-

Function:- QSort( array, first, last) where,
          array:- listof element,
          first:- position of 1st element in list,
          last:- position of last element in list.

Step1 :- Initialize.
               low = first
              high = last
              pivot = arry [ (low + high) /2]

Step2 :- Repeat through step7 
            while ( low <= high)

Step3 :- Repeat step4
           while ( Array[ high] < pivote)

Step4 :- low = low+1

Step5 :- Repeat step6
           while( array [high] < pivote)

Step6 :-  high = high-1

Step7 :- if low <= high
            i> temp = array [low]
           ii> array[low] = array[high]
           iii> array[high] = temp
          iv> low = low+1
          v> high = high -1

Step8 :- if  first < high
         QSort ( array, first, high)

Step9 :- if first < last
          QSort ( array, low, last)

Step10 :- Exit.

  ⇰  PROGRAM OF QUICK SORT :- 

# include <stdio.h>

# include <conio.h>

void Qsort(int array[ ] , int first , int last)

{

   int temp, low, high, pivot;

       low = first;

       high = last;

   pivot = array [ (first + last) /2];

do

   {

        while ( array [ low ] < pivote )

           {

                low ++ ;

           }

      while ( array [ high ] > pivote)

          {

                high -- ;

          }

    

if ( low <= high )

     {

         temp = array [ low ];

         array [low ++ ] = array [ high ];

         array [ high-- ] = temp;

      }

    } while ( low <= high) ;

    if ( first < high)

           Qsort ( array, first, high)

   if ( low < last)

          Qsort ( array, low, last)

}   

 void main ()

  {

      int value [5] , i;

      printf(" \n Enter values for sort:- ");

        for( i = 0 ; i < 5 ; i++)

       {

          scanf("%d", & value[i] );

       }

  Qsort (value, 0, 4);

  printf( "\n Sorted value :- ");

     for( i =0 ; i< 4; i++) 

    {

         printf(" \t %d" , value [i]);

    }

     getch();

}

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