1) The document discusses two common search algorithms: sequential search and binary search. Sequential search looks at each item in a list sequentially until the target is found. Binary search works on a sorted list and divides the search space in half at each step. 2) It provides pseudocode examples of how each algorithm works step-by-step to find a target value in a list or array. 3) Binary search is more efficient than sequential search when the list is sorted, as it can significantly reduce the number of comparisons needed to find the target. Sequential search is used when the list is unsorted.

1. DATA STRUCTURE
Chapter 4: Basic Search
Algorithms
Prepared & Presented by
Mr. Mahmoud R. Alfarra
2010-2011
College of Science & Technology
Dep. Of Computer Science & IT
BCs of Information Technology
http://mfarra.cst.ps

2. Out Line
 Introduction
 Sequential Search Algorithm
 Binary Search Algorithm
 Which is the best ?
 Search and sorting in Array List
2

3. Introduction
 Searching for data is a fundamental computer
programming task and one that has been
studied for many years.
 There are two fundamental ways to search for
data in a list: the sequential search and the
binary search.
3

4. Sequential Search
Algorithm
4
 The most obvious type of search is to begin at
the beginning of a set of records and move
through each record until you find the record
you are looking for or you come to the end of
the records. This is called a sequential search.
 A sequential search (also called a linear
search) is very easy to implement.

5. Sequential Search
Algorithm
5
2 5 81 88 90 99
7 9 34 55 56 66 79 80
1 2 3 4 5 6 7 8 9 10 11 12 13
Wanted = 80
array
0
==
‫؟‬
.... ....
The wanted value at comparison number 10 and position 9

6. Sequential Search Algorithm
6
1. static void Main(string[] args)
2. { int[] a = { 10, 2, 34, 4, 3, 1, 100 };
3. int wanted = 1;
4. int target_index=-1;
5. for (int i = 0; i < a.Length; i++)
6. if (a[i] == wanted) {
7. target_index = i;
8. break; }
9. if (target_index >= 0)
10. Console.WriteLine(" The wanted value exist at
position: "+(target_index+1)+"'th");
11. Console.Read(); }
Practice: Reprogram
this problem using
string data.

7. Binary Search Algorithm
7
 When the records you are searching through
are sorted into order, you can perform a more
efficient search than the sequential search to
find a value. This search is called a binary
search.
 To use this algorithm, we first need our data
stored in order (ascending, preferably) in an
array.

8. Binary Search Algorithm
8

9. Binary Search Algorithm
9
2 5 81 88 90 99
7 9 34 55 56 66 79 80
1 2 3 4 5 6 7 8 9 10 11 12 13
(0+13) / 2 = 6
If (array[6] == 80)
return 6
Elseif (array[6] > 80)
High = 6 -1
Else
Low = 6+1
Middle = (low + high)/2
Wanted = 80
array
0
(7+13) / 2 = 10
If (array[10] == 80)
return 10
Elseif (array[10] > 80)
High = 10 -1
Else
Low = 10+1
(7+9) / 2 = 8
If (array[8] == 80)
return 8
Elseif (array[8] > 80)
High = 8-1
Else
Low = 8+1
1 2 3

10. Binary Search Algorithm
10
2 5 81 88 90 99
7 9 34 55 56 66 79 80
1 2 3 4 5 6 7 8 9 10 11 12 13
Middle = (low + high)/2
Wanted = 80
array
0
(7+9) / 2 = 8
If (array[8] == 80)
return 8
Elseif (array[8] > 80)
High = 8-1
Else
Low = 8+1
3
(9+9) / 2 = 9
If (array[9] == 80)
return 8
Elseif (array[9] > 80)
High = 9-1
Else
Low = 9+1
4
return 8

11. Binary Search Algorithm
11
‫البيانات‬ ‫تراكيب‬ ‫مساق‬
‫إعداد‬ ‫العلمية‬ ‫المادة‬
/
‫أ‬
.
‫ا‬ َّ‫الفــر‬ ‫رفيق‬ ‫محمود‬
1. static void Main(string[] args) {
2. int[] a = { 2, 3, 5, 8, 10, 23, 30};
3. int wanted = 23;
4. int start = 0;
5. int last = a.Length - 1;
6. int middle = (last + start) / 2;
7. int result =0;
8. while (start < last) {
9. middle = (last + start) / 2;
10. if (a[middle] == wanted) {
11. result = 1;
12. break; }
13. else if (a[middle] < wanted)
14. start = middle + 1;
15. else
16. last = middle - 1; }
17. if (result == 1)
18. Console.WriteLine("The wanted element is exist at: " +
middle);
19. else
20. Console.WriteLine("The wanted element does not exist ");
To understand:
trace step by step
To practice: try with
string data
More practice: try with
2-D array

12. Which is the best ?
12
 Sequential search is used when the items in
the list are in random order.
 Binary search is used when the items are
sorted in the list.

13. Search and sorting in Array List
13
1. static void Main(string[] args) {
2. ArrayList a = new ArrayList();
3. a.Add(20);
4. a.Add(4);
5. a.Add(3);
6. a.Sort();
7. int result = a.BinarySearch(3);
8. Console.WriteLine(" position of 3 at : " + result);
9. result = a.BinarySearch(7);
10. Console.WriteLine(" position of 7 at : " + result);
11. Console.WriteLine();
12. foreach (object x in a)
13. Console.WriteLine(" " + x);
14. Console.ReadLine(); }

14. Thank You …
14
Remember that: question is the key of knowledge

15. Ahl Eljanna 

َ‫ق‬َ
‫د‬َ
‫ص‬ ‫ي‬ّ
‫ذ‬‫ه‬‫ل‬‫ا‬ ّ‫ه‬ّ
‫َلِل‬ ُ
‫د‬‫ح‬
‫م‬َ‫ح‬
‫ْل‬‫ا‬ ‫وا‬ُ‫ل‬‫ا‬َ‫ق‬َ
‫و‬
‫ا‬ ‫ا‬َ‫ن‬َ‫ث‬َ
‫ر‬‫ح‬
‫َو‬‫أ‬َ
‫و‬ ُ‫ه‬َ
‫د‬‫ح‬‫ع‬َ
‫و‬ ‫ا‬َ‫ن‬
ُ‫أ‬‫ه‬
‫و‬َ‫ب‬َ‫ت‬َ‫ن‬ َ
‫ض‬‫ح‬
‫ر‬َ‫ح‬
‫ْل‬
َ
‫م‬‫ح‬‫ع‬ّ‫ن‬َ‫ف‬ ُ‫اء‬َ
‫ش‬َ‫ن‬ ُ
‫ث‬‫ح‬‫ي‬َ
‫ح‬ ّ
‫هة‬‫ن‬َ‫ح‬
‫ْل‬‫ا‬ ‫ح‬
‫ن‬ّ
‫م‬
َ
‫ي‬ّ‫ل‬ّ
‫ام‬َ
‫حع‬‫ل‬‫ا‬ ُ
‫ر‬‫ح‬
‫َج‬‫أ‬
15