� Structure of Indexes

� Linear Searching

� Binary Searching

Dr. Hussien M.

Sharaf2

Dr. Hussien M.

Sharaf3

Structure of Indexes

� Indexes must be sorted on ascending or descending order with respect to a (one or more ) field(s).

CompanyName offset

Google 211Record1

\n

\n

IBM 0Record2 \n

ITE 643Record3 \n

Microsoft 462Record4 \n

Apple Mac 985New

record\n

Dr. Hussien M.

Sharaf4

Given the following file, build an index for company names.

File contents:

ID, Name, Phone, comment\n

5, Google, 2133 7710, 5 branches\n

7, ITE, 24413 9900, 1 branch\n

8, Microsoft, 2789 0054, 9 branches\n

9, IBM, 24413 9900, 5 branches\n

10, Apple Mac, 2567 9876, 8 branches\n

Dr. Hussien M.

Sharaf5

Step:1 write down the offset of each record .

Company Name , offset

Google , 26

ITE ,60

Microsoft , 90

IBM ,127

Apple Mac , 158

Dr. Hussien M.

Sharaf6

Step:2 Reorder the records by company name.

Company Name , offset

Apple Mac , 158

Google , 26

IBM ,127

ITE ,60

Microsoft , 90

Dr. Hussien M.

Sharaf7

� int LinearSearch(TargetName)◦ For each element in Index collection:

◦ {� If Index[i].CompanyName==TargetName

� {

� Return Index[i].offset

� }

◦ }

◦ Return -1 //not found

Dr. Hussien M.

Sharaf8

� int BinarySearch(TargetName)

� { int low=0,high=Index.size();

� Midpoint=(high+low)/2;

� while (low<=high)◦ {CurrentRecordIndex=Index[Midpoint];

◦ If (CurrentRecordIndex.CompanyName==TargetN

ame) � Return CurrentRecordIndex.offset

Dr. Hussien M.

Sharaf9

◦ If (CurrentRecordIndex.CompanyName==TargetName) � Return CurrentRecordIndex.offset

◦ If (CurrentRecordIndex.CompanyName<=Targetname)

� Search in the right half: low= Midpoint+1

◦ Else

� Search in the left half: high= Midpoint-1

◦ } //end while

◦ Return -1 //not found

Dr. Hussien M.

Sharaf10

◦ Searching should be on a collection loaded in main memory

◦ Binary search O(logn) is faster than Linear search O(n)

◦ The penalty of using Binary search is that the collection must be sorted.

◦ Is this a problem for an Index?

� Implement linear search on IndexesCollection class.

� Implement Binary search on IndexesCollectionclass.

Dr. Hussien M.

Sharaf11