describes all searching and sorting techniques related to computer science engeneering

1. Prepared by,
DAVID RAJU KOLLURI
Diploma[CSE], B.Tech[CSE], M.Tech[CSE], (PhD[CSE])
Associate Professor, Dept of CSE
KESHAV MEMORIAL INSTITUTE OF
TECHNOLOGY
AN AUTONOMOUS INSTITUTION -
ACCREDITED BY NAAC WITH 'A' GRADE
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AUTONOMOUS COLLEGE
UNIT-IV
SEARCHING & SORTING

2. SEARCHING
Definition: The process of finding an element, whether it is
present in the given list or not is called searching
 Searching for items is one of the most critical activities
in many applications.
 Examples of few search activities are spell checking,
searching for a name in list of names, opening files
etc.
The efficiency of a search depends on three things.
 The size and organization of the collection of data we
are searching.
 The search algorithm that is used.
 The efficiency of the test used to determine if the
search is successful.

3. Typesof Searching
 We will describe two searching methods in this
session.
 Linear Search: which starts searching from the
beginning of the list and checks each element until a
match is found.
 Binary search: which can only be used on a sorted
list. It successively divides the array into two parts,
then discards the part that cannot contain the
element we are searching for.

4. Searching involves following:
 Search List: The search list is simply a common
term for the collection of elements that we are
storing in. The elements in the list may or may
not be ordered (ascending or descending).
 Target Element: The element that we are
searching for. (Sometimes referred to as key
element).

5. Linear Search (Sequential Search):
 Linear Search is the traditional method of
searching. It is very simple but very poor in
performance at times.
 We begin search by comparing the first element
of the list with the target element. If it matches,
the search ends. Otherwise, we will move to next
element and compare. In this way, the target
element is compared with all the elements until a
match occurs.
 If the match do not occur and there are no more
elements to be compared, we conclude that
target element is absent in the list.

6. Linear Search
Successf
ul
KEY/TARGET
Element
Successful Search at
Position: 6

7. Linear Search(Function)
int LinearSearch(int a[ ] , int n, int key)
{
int i = 0;
while(i<n)
{
if (a[i] == key)
return(i);
i++;
}
return (-1);
}

8. performance for Linear search list of N items.
CASE MEANING NUMBER OF
ITERATION
TIME
COMPLEXITY
CASE
Best The item to be
searched is the
first item in the list
1 (1) Best
Average The item to be
searched is found
some where close
to middle of list
N/2 (N) Average
Worst The item to be
searched is the last
item in list, or it
does not exist at all
N (N) Worst

9. Binary Search:
 Binary Search is a vast improvement over the linear search but it
cannot always be used.
 For binary search to work, the items in the list must be in a sorted
order (either increasing (ascending) or decreasing (descending)
order similar to the way words in a dictionary are arranged.
 The pre-requisite for Binary Search method is that the input
elements list must be in the sorted order.
 The method starts with looking at the middle of the list. If it
matches with the target element, then the search is complete
Otherwise, the target element may be in the upper half or lower
half. The search progresses with the upper half if the target
element is greater than the middle element or with the lower half if
the target element is less than the middle.
 The process is continued until the target element is found or the
portion of the sub list to be searched is empty.

10. Binary Search
 Mid Point Calculation:
 Mid = (Low + High) / 2;
 If(Key == A[Mid]) then, return Mid+1;
 If(Key < A[Mid]) then Update High(High = Mid -
1)
 If(Key > A[Mid]) then Update Low(Low = Mid +
1)
Low Mid High
Key < A[Mid] Key > A[Mid]
0 1 2 3 4 5 6 7

11. Binary Search:
Mid = (Low +
High)/2;
High
Low
Target/Key
Element 23 Found at 6th(5+1)
Position

12. Binary Search:
int BinarySearch(int a[], int n, int key)
{
int low, high, midpos;
low = 0; high = n-1;
while(low <= high)
{
midpos = (low+high)/2;
if (key = = a[midpos])
return(midpos);
else
if(key<a[midpos])
high = midpos –1;
else
low = midpos + 1;
}
return(-1);
}
Key = 23
Total No of Comparisons
are: 3

13. Binary Search:
int r_binarysearch( int a[], int key, int low, int high)
{
int mid;
if (low>high)
return (-1)
mid = (low +high)/2;
if ( key = = a[mid])
return(mid);
if (key < a[mid])
r_binarysearch( a, key, low, mid-1);
else
r_binarysearch( a, key, mid+1,high);
}
Key = 23
Total No of Comparisons
are: 3

14. Binary Search:
 The recursive function determines whether the
search key lies in lower or upper half of the
array, then it calls itself on appropriate half.
 Each step of algorithm divides the list into two
parts and the search continues in one of them
and other is discarded.
 The search requires at most k steps where
2kn which results in time complexity of k =
log2n i.e., O(log n) for average and worst
cases.

15. Sorting Techniques
Definition:
 The process of getting data elements into order is called
Sorting.
 We have different techniques in Sorting
 Exchange Sort(Bubble Sort)
 Selection Sort
 Insertion Sort
 Quick Sort
 Merge Sort
 Tree Sort
 Radix Sort

16. Exchange Sort(BUBBLE SORT)
 Fundamental Mechanism: in an exchange sort is to
repeatedly make comparisons, and if required, swap
adjacent items. Bubble Sort is an example of the
exchange sort technique.
 Bubble Sort Process:
Always Adjacent two elements will be compared, if
required . At the end of the each and every pass
Largest/Smallest Element will be bubbled to Last(End)
Position

17. BubbleSort Mechanism
No of COMPARISIONS in each and every PASS

18. BubbleSort Mechanism

19. BubbleSort forStrings & Integers:
Bubble Sort for Strings:
void bubble_sort(char *str; int length)
{
for(i=0; i<length; i++)
for(j=i+1; j<length;j++)
{
if (str[i]>str[j])
{
temp = str[i];
str[i] = str[j];
str[j] = temp;
}
}
printf(“Sorted String is %sn”,str);
}
Bubble Sort for Integers:
bubblesort(int a[], int n)
{
int pass, j, noexchange;
for(pass=0;pass<n-1;pass++)
{
noexchange=1;
for(j=0;j<n-pass-1;j++)
{
if(a[j]>a[j+1])
{
swap(a[j]>a[j+1]);
noexchange = 0;
}
}
if (noexchange);
return;
}
}

20. Sorting Techniques
Definition:
 The process of getting data elements into order is called
Sorting.
 We have different techniques in Sorting
 Exchange Sort(Bubble Sort)
 Selection Sort
 Insertion Sort
 Quick Sort
 Merge Sort
 Tree Sort
 Radix Sort
Out of Syllabus

21. Selection Sort:
 Assume First Element as Min element( Assumed
Minimum)
 Using Selection Sort, the Assumed Min is compared
with the remaining n-1 items, and whichever of all is
lowest, is called Actual Min will be used to swap the
Assumed Min.
 Then the second item from the list is taken and
compared with the remaining (n-2) items, if an item with
a value less than that of the second item is found on the

22. Selection Sort:
Sorting Completed

23. Selection Sort:
Function to perform Selection Sort:
void selection_sort(char *str, int len)
{
int i, j, min, swap;
char temp;
for(I=0; I<len; I++)
{
swap = 0;
min=I;
strcpy(temp , str[I]);
for (j = I+1; j<len; j++)
{
if( strcmp(str[j] ,temp)<0)
{
min=j;
strcpy(temp , str[j]);
swap =1;
}
}
if (swap)
{
strcpy(str[min] ,str[i]);
strcpy(str[i] ,temp);
}
}
}

24. Insertion Sort:
 Insertion sort is a simple sorting algorithm that
works the way we sort playing cards in our
hands.

25. Insertion Sort:
void insertionSort(int arr[], int n)
{
int i, key, j;
for (i = 1; i < n; i++)
{
key = arr[i];
j = i - 1;
/* Move elements of arr[0..i-1], that are
greater than key, to one position ahead
of their current position */
while (j >= 0 && arr[j] > key)
{
arr[j + 1] = arr[j];
j = j - 1;
}
arr[j + 1] = key;
}
}