Chapter 4: basic search algorithms data structure

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