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Copy of Lesson 2 - Searching Algorithms
2
Revision - 2.1 Searching Algorithms
E- LEARNING
Revise, Recap, Review
Objectives
3 aspects of computational thinking
2 registers used in fetch, decode, execute cycle
The name of the register used to store the address of the next instruction in the cycle
Lesson Objectives
To understand how to write algorithms using flow diagrams
To understand how a linear search works
To understand how a binary search works
Flow Diagrams
A flow diagram is a visual representation of how an algorithm works.
There are 5 symbols you will need to know for your exam that will enable you to draw these
Theory
Start/End
At the beginning and end of your algorithm you will need boxes with rounded corners
Inputs/Outputs
Any inputs or outputs (print statements) go in a parallelogram box
Actions/process
Rectangular boxes represent an action or process i.e. wages = wages * 1.1
Decisions
Diamond shaped boxes are used to store decisions - these are your IF statements and loops!
Sub routines
A sub routine (functions and procedures) go in boxes like this
Task
Task
Create a flow diagram for an algorithm that:
- Accepts a movie running time in minutes
- Converts minutes to seconds
- Prints out the total
WAGOLL
Hexadecimal
This is a number system that we will learn more about later, but instead of the 10 symbols we use in decimal (0-9) there are 16 symbols.
0-9 have the same value in hex as they do in decimal, but we have 6 further symbols:
A = 10
B = 11
C = 12
D =13
E = 14
F = 15
Task
Create a flow diagram for an algorithm that:
Accepts a number between 0 - 15
Converts the number into hexadecimal
Prints the result
WAGOLL
Searching Algorithms
Searching
You need to know about two algorithms that search for information - the linear search and the binary search
Linear Search
Easy to understand!
A linear search looks at each item in the list and checks if it is what we are looking for! If not, we check the next item and so on.....
Binary Search
Can only work on a list that is in order
Looks at middle item (length of list + 1 / 2)
If the middle item is too big, get rid of the second half, if it's too small, get rid of the first half
Binary Search
Now you have a list half of the size to search!
Repeat the process until you've found what you are looking for!
YouTube Strangeness....
Exam Questions
Likely to ask you to search a list in the exam paper using either of these methods
OR to explain how they work, so you need to know HOW they work