Quick Sort
- a recursive divide and conquer
algorithm
10
8
20
16
Created by: Marifel C. Toledo
19
8
1
10
16
19
20
Did you
know?
Why
it is the
best?
In most cases Quick
Widely used as the Sort
Sort Is the best
function of many
comparison sorting
Less Memory
algorithm.
programming
Fast
languages.
2
1-PIVOT
Steps
2-PARTITION
“pivot” is the arbitrary element in the collection
•
•
Rearrange the array elements in such a
way that the all values lesser than the pivot
Selection of the proper pivot will improve
should
come
before the pivot and all the
•
Pick
a
Pivot
–
(random
or
median)
the efficiency of the algorithm.
values greater than the pivot should come
Median of three partition is the most
after it.
popular method in choosing a pivot. It uses
pivot as the median of
the left most,
right • into
This 2
method
is called partitioning the
• Partition
elements
sections:
most, or the middle element
of the
array.
the end of the partition function,
-elements<to
pivotAt(left)
list/array.
the pivot element will be placed at its
-elements>tosorted
pivotposition.
(right)
•
1
2
3
•
• Recursively Quick Sort the two halves
3-RECURSION
down until
sorted – (down to 1 element)
Do the above process recursively to all the sub-arrays and sort the
3
elements.
Key to Quick Sort’s
Efficiency
1. Properly pick the Pivot
2. Quick Sort works best on UNSORTED
lists or arrays.
4
EYES
EYES HERE!
HERE!
EYES
HERE!
TEST CASE:
Input data:
41
25
25
25
25
41
25
25
25
41
62
SAMPLE PROGRAM
41>13?
98>62?
25>13?
62>41?
41>98?
j-41>62?
i
=
41>25?
Pivot
j-i++
Pivot
=j j = i
98
25
13
41
13
41
62
41
62
62
62
41
62
i
Pivot
13
62
13
13
41
1398
41
13
13
13
13
13
j
98
25
62
62
62
41
25
62
25
41
62
41
6213
98
98
98
25
98
98
98
98
98
j
j
ijj
iii i
j
j
i=
jjj than
i 98
Sorted
Pivot
25data:
Numbers
lessii than
Numbers greater
TRUE
pivot
or equal to pivot
TRUE
FALSE
FALSE
TRUE
TRUE
62
98
41
13
25
13
25
41
Pivot
=
41
Pivot
=
41
 The illustration shows how quicksort works.
98
62