It slearning 365 Limited. 36 Richardson Close Broughton Astley. Leicestershire LE9 6NU. First Edition

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2 Copyright 2014 it slearning 365 Limited All rights reserved. Reproduction, distribution, or transmission of this material, including photocopying, recording, or other electronic or mechanical methods is granted to subscribers of the It slearning 365 Learning Gateway and Learning Library. It slearning 365 Limited 36 Richardson Close Broughton Astley Leicestershire LE9 6NU First Edition

3 ALGORITHM In computing an algorithm is a step by step procedure for calculations. Algorithms are used for calculation, data processing, and automated reasoning. Basically an algorithm is a set of instructions for performing a calculation. An algorithm will need a set of Inputs. It will perform some calculations and instructions based on these inputs and will produce an Output. Fact File Jon Von Neumann was born on the 28 th December 1903 in Budapest. He spent most of his working life in the United States teaching at Princeton University and the Institute for Advanced Study in Los Alamos where he specialised in mathematics, physics, statistics and economics. In 1945 he developed the Merge Sort Algorithm. 1

4 WRITING ALGORITHMS Algorithms can be written and planning in different form, including: Normal Writing Pseudocode Flowcharts Programming languages Control Tables Normally algorithms are designed using flow charts and pseudocode. These are easy for us to understand. They are then coded into a Programing Language for a computer system to understand. 2

5 COMPUTER ALGORITHMS In computer systems an algorithm is a set of instructions written in a software language. An algorithm is different to Modules, Functions and Procedures. Modules are separate parts of a program. When the program code is compiled and linked the different modules are brought together to form the whole piece of software. A Function is a named section of the program that performs a specific task. Different functions can be combined together into a Module. A Procedure is a routine or subroutine of a Function. A number of procedures can be combined together to form a Function. Algorithms form part of a Procedure. A procedure to sort a membership database into membership renewal date could include a Bubble Sort Algorithm for example. 3

6 BUBBLE SORT The simplest type of algorithm is called the Bubble Sort. The algorithm repeatedly runs through the list of number to be sorted. Each number is compared with the previous and next number to check to see if they are in the correct order. If two numbers are in the wrong order the algorithm will swap them. 4

7 The big advantage of using a Bubble Sort is that the algorithm is able to tell when the list has been sorted. However, if you have a large list of data to sort, the Bubble Sort Algorithm can be slow. Function bubblesort Inputs: array 'a' of size 'N' Local variables: j, t DO t = a[ 0 ] FOR j = 1.. N 1 IF a[ j - 1 ] > a[ j ] Swap a[ j ] and a[ j - 1 ] END IF END FOR WHILE t not equal to a[ 0 ] End Function 5

8 MERGE SORT A Merge Sort is a more complicated type of algorithm which divides the data into smaller lists, sorts the lists into order and then merging them to form larger lists. The algorithm works by splitting the data into two lists. It then uses the Bubble Sort Algorithm on each list to sort them into order. Next it compares the first value from both sorted lists and placing the smallest of the two at the start position of the new list. 6

9 The algorithm then moves onto the next number in the sub list that has lost a value, performs the same comparison and moved the smallest number into the new list. 7

10 BUCKET SORT The Bucket Sort is sometimes called the Bin Sort. It works by splitting the set of data into a number of buckets. Each bucket is given an upper and lower boundary and the original list is split based on these boundaries. 8

11 Each bucket is then sorted individually using the Bubble Sort Algorithm. Finally both lists are combined to provide the final sorted list. 9

12 SHELL SORT The Shell Sort algorithm works by comparing numbers in a list and moving and inserting numbers as necessary. The algorithm works by sorting through the list in increments. The increment is calculated by dividing the number of values in the list by 2 (and rounding to the next whole number). If the increment is 7, the algorithm with compare the first and 8 th number. If the 8 th number is larger than the first it will leave them and move on to the 2 nd and 9 th numbers. If the 1 st number is larger than the 8 th number the algorithm will swap them before moving onto the 2 nd and 9 th numbers. 10

13 When the list has been sorted for the first time, the increment is calculated again by dividing the original increment by 2. The sort is then completed again. This process is repeated until an increment of 1 is reached and the list is sorted into order. 11

14 QUICK SORT The Quick Sort algorithm divides the data into two lists. To do this it first needs to find the middle value in the list. This is known as the Pivot Value. The algorithm then sorts the values into two lists based on the Pivot Value the first list containing values which as less than the Pivot Value and the second list containing values which are greater than the Pivot Value. The algorithm reads through the list starting at the first value until it finds a value that is Greater Than or Equal To the Pivot Value. It then starts with the last value in the list and reads back though the list until it finds a value that is Less Than or Equal To the Pivot Value. 12

15 When it has found these two values it swaps them. This process continues until all the values are in the correct order. 13

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