1.3 algorithms

Question 1

o(n)

Answer 1

the time is takes is directly proportional to the size of the data

Question 2

o(1)

Answer 2

always takes the same time and the same number of steps (memory) regardless of the amount of data input

Question 3

o(n^2)

Answer 3

as the number of items steadily increases, the time taken increases more rapidly therefore, the curve gets steeper

Question 4

o(2^n)

Answer 4

time doubles for each addition to the data set - time is increasing exponentially

Question 5

o(log2n)

Answer 5

as the number of items steadily increases, the time taken increases by smaller and smaller amounts

Question 6

o(nlog2n)

Answer 6

divide and conquer
the graph is like a massive quadratic with less of a curve

Question 8

explain the purpose of procedures (sub-routines)

Answer 8

• algorithms/programs can be broken down into smaller parts
• these are names reusable pieces of code that can be called any number of times within an algorithm/ program to perform a specific task
• procedures are used to avoid the duplication of code
• each procedures can be individually tested/ debugged
• procedures are used to make an algorithm/program more efficient and secure (try not to use this point)

Question 9

the difference between local and global variables

Question 11

what is meant by passing by reference and why is it used

Answer 11

• where a address is passed via a parameter into a subroutine and the original value is passed and used by that subroutine
• this is used if any changes made in the subroutine needs to be stored in the original value/variable outside the subroutine

Question 12

what is meant by passing by value and why is it used

Answer 12

• where a value is passed via a parameter into a subroutine and a copy of the value is created for the duration of the subroutine cell
• this ensures that the original value passed to the subroutine cannot be changed

Question 13

why is self documenting identifiers important and give an example

Answer 13

• allows code to be followed and understood more easily
• reduces the need for the additional documentation to be produced, such as additional annotation or software manuals
• example: VAT or firstname

Question 14

why is program layout important and give an example

Answer 14

• allows blocks of code and constructs to be followed and identified more easily
• a consistent program layout helps improve the quality of the software and allows developers to maintain quality and standards
  -example: indentation to identify the start and end of constructs such as IF statements, Loop/nested loop structures

Question 15

why is annotation is important and give an example

Answer 15

• allows developers to record the development process and logic with the actual code
• many developers could be working on the one project and each developer needs to understand the logic between one and others code
  -example: X DIV 2 ‘calculates if X is even or odd

Question 16

why is it good programming practice to use constants, meaningful names for variables and annotation in computer programs

Answer 16

• they can be set once and then used many times throughout the program and if they change then they only have to be changed once. (constants)

-it is clear what the variable is holding and aids program readability (meaningful names)

-other programmers will find the code easier to follow (annotation)

Question 17

benefit of passing by value

Answer 17

• avoids problem of unintended side affects where the parameter has its value changed in the main program as well as in the procedure

Question 18

benefit of passing by reference

Answer 18

• avoids the larger amount of processing/storage (associated with passing by value, possibly large amounts of copying)
  -allows change to be passed back to the calling program

Question 19

what is the purpose of validation and give an example

Answer 19

• is the process of checking if the data entered is sensible in the context in which it is being used
  -reduces the possibility of entering invalid data into a system

example:
range checks on dates

Question 20

2 situations where a linear search will generally perform faster than a binary search

Answer 20

1. when the number of items to be searched is very small
2. the search value is one of the first items in the array

Question 21

1 situation where a binary search will generally perform faster than a linear search

Answer 21

• when there is a large sorted data set