Computing Concepts

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Computing Concepts

• Searching and Sorting

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What we have done so far in data structures

• data structure as a way of organising the storage
  of data
• brief look at
• records
• arrays
• sequences (lists, queues, stacks)
• trees

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What we have done so far in data structures

• Done more on
• records
• arrays

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Example

• What are the contents of the element in the array
  PlayOffTeams which has index 3 ?
• What is the value of PlayOffTeams2 ?

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Example

• Describe completely the structure of the array
  PlayOffTeams.

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Example

• The index for the array PlayOffTeams lies in the
  range 1..4
• The elements are of type Name

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Example

• Write a fragment of Pascal that would display the
  third name in the array.
• WriteLn(PlayOffTeams3)

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Example

• Write a fragment of Pascal that would display all
  the names in the array.

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Example

• FOR I 1 TO 4 DO
• BEGIN
• WriteLn(PlayOffTeamsI)
• END

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What we shall do today

• Look at arrays in Pascal (not on assessment)
• Search arrays
• Sort (re-order) arrays

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Pascal Array

• X1 gets 2
• X2 gets 4
• X3 gets 6 etc

Prog1_BigArray
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Searching an array

• Example
• How does hole in the wall find your account from
  your credit card details ?
• Need to search through the array of bank records

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Different kinds of search available

• Linear Search
• Binary search

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Linear Search

• Searching for a birthday day of the month
• Searching for bank records
• 1,000 bank records
• Fastest find in -
• 1 comparison
• Slowest find in -
• 1,000 comparisons
• Average find in
• 500 comparisons

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Binary Search

• How can we speed up the process ?
• Binary search for a number in range 1 to 1000
• Searching for a birthday day of the month

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Sorting

• We need to sort to
• be able to use the fast binary search
• produce reports in required order

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Sorting

• Many different ways of carrying out a sort on an
  array.
• We shall examine EXCHANGE SORT (Also known as the
  BUBBLE SORT)
• We shall look at others

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Exchange Sort

• Simple
• Slow
• Demo with heights
• Demo with birthday day of the month

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Pascal Exchange Sort

• Prog3_LittleSort
• 10,000 elements
• 20,000 elements
• 40,000 elements

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Sorting Demos

• http//www.cs.ubc.ca/spider/harrison/Java/sorting-
  demo.html

• http//www.cs.hope.edu/alganim/animator/Animator.
  html