Algorithm to sort a given list by quick sort method, Data Structure & Algorithms

Q. Write down an algorithm to sort a given list by making use of Quick sort method. Describe the behaviour of Quick sort when input given to us is already sorted.                                  

Ans.

Algorithm for Quick Sort is written below

QUICK(A, N, BEG, END, LOC)

Here A is an array with N element. Parameter BEG

and END comprises the   boundary value of the sub

list of A to which this method applies. LOC keeps track of the position of the first element A[BEG] of the sublist during the particular procedure. The local varrible LEFT     and  RIGHT will contain the boundary value of the list elements that have not been scanned.

1. [Initialize]   Set LEFT:=BEG, RIGHT;=END and LOC:=BEG.

2. [Scan from left to right]

(a) Repeat while A[LOC] <=A[RIGHT] and LOC!=RIGHT; RIGHT:=RIGHT-1; [End of loop]

(b)If LOC= RIGHT, then Return;

(c)If A[LOC ] > A[RIGHT],then: [Interchange    A[LOC] and A[RIGHT]] TEMP:=  A[LOC]  ,A[LOC] =  A[RIGHT] , A[RIGHT] :=TEMP;

(i) Set LOC =RIGHT

(ii)      Go to step 3

3.[Scan from left to right]

repeat while A[LEFT] <=A[LOC] and  LEFT!= LOC; LEFT := LEFT +1; [End of loop]

(a) If LOC  =LEFT, then Return;

(b) If  A[LEFT]  > A[LOC] ,then

(i) [Interchange A[LEFT]  and A[LOC]] TEMP:=A[LOC],A[LOC]:=A[LEFT] . A[LEFT]:= TEMP

(ii) Set LOC :=LEFT (iii) Go to Step 2; [End of if structure]

(Quicksort) This algorithm sorts an array A with N elements.

1. [Intialize.] TOP := NULL

2. [Push boundary values of A onto stacks when A has 2 or more elements.]

If  N>1, then: TOP+1,LOWER [1]:=1, UPPER [1]: =N

3. Repeat steps 4 to 7 while TOP != NULL.

4. [Pop sublist from stacks.]

Set BEG: =LOWER[TOP], END:=UPPER[TOP], TOP:=TOP-1.

5. Call QUICK (A, N, BEG, END, LOC). [ Push left

sublist onto stacks when it has 2 or more elements.]

If BEG < LOC -1, then:

TOP:= TOP+1, LOWER[TOP] := BEG, UPPER[TOP]= LOC -1.

[End of If structure.]

6. [Push right sublist onto stacks when it has 2

or more elements.]

If  LOC +1< END , then:

TOP := TOP+1, LOWER[TOP] := LOC +1, UPPER[TOP] := END.

[End of If structure .] [End of Step 3 loop.]

7. Exit.

The behaviour of quick sort when the list is sorted is of order O(n2) as this is the worst case for quicksort

Posted Date: 7/13/2012 2:15:20 AM | Location : United States







Related Discussions:- Algorithm to sort a given list by quick sort method, Assignment Help, Ask Question on Algorithm to sort a given list by quick sort method, Get Answer, Expert's Help, Algorithm to sort a given list by quick sort method Discussions

Write discussion on Algorithm to sort a given list by quick sort method
Your posts are moderated
Related Questions
What is called the basic operation of an algorithm? The most significant operation of the algorithm is the operation contributing the most to the total running time is known as

Define null values.  In some cases a particular entity might not have an applicable value for an attribute or if we do not know the value of an attribute for a particular entit

7. String manipulation 7.a Write a C Program using following string manipulation functions a) strcpy b) strncpy c) strcmp d) strncmp e) strlen f) strcat

Binary: Each node has one, zero, or two children. This assertion creates many tree operations efficient and simple. Binary Search : A binary tree where each and every left

Merge sort: Merge sort is a sorting algorithm that uses the idea of split and conquers. This algorithm splits the array into two halves, sorts them separately and then merges t

A LGORITHM (Deletion of an element from the linked list) Step 1  Begin Step 2  if the list is empty, then element cannot be deleted Step 3  else, if the element to be del

how do we use 4-discs stack to solve tower of hanoi problem and write an algorithm to solve it?

Using stacks, write an algorithm to determine whether the infix expression has balanced parenthesis or not Algorithm parseparens This algorithm reads a source program and

W h at are the different ways by which we can represent graph?  Represent the graph drawn below using those ways.     T he d iff e r e nt w a y s by

What is String Carrier set of the String ADT is the set of all finite sequences of characters from some alphabet, including empty sequence (the empty string). Operations on s