Algorithms

Question 1

What is decomposition?

Answer 1

Breaking a complex problem down into smaller problems and solving each one individually

Question 2

What is abstraction?

Answer 2

Picking out the important parts of information from the problem, ignoring the specific details that don’t matter

Question 3

What is algorithmic thinking?

Answer 3

A logical way of getting from the problem to the solution

Question 4

What are algorithms?

Answer 4

Sets of instructions for solving a problem

Question 5

What are the advantages of pseudo-code?

Answer 5

1) quick to write

2) can be easily converted into any programming language

Question 6

How can algorithms be shown?

Answer 6

1) pseudo-code

2) flowcharts

Question 7

What box is used to show the beginning and the end of an algorithm?

Answer 7

Boxes with rounded corners

Question 8

What box is used to show anything that’s put into or taken out of the algorithm?

Answer 8

Parallelogram boxes

Question 9

What box is used to show general instructions, processes and calculations?

Answer 9

Rectangular boxes

Question 10

What box is used to show decisions, often a ‘yes’ or ‘no’ question?

Answer 10

Diamond boxes

Question 11

What are subroutine boxes references to?

Answer 11

Other flowcharts

Question 12

What do the arrows in flowcharts show?

Answer 12

The direction you should follow

Question 13

What can flowcharts show?

Answer 13

1) sequences
2) selections
3) iterations

Question 14

What type of lists are binary searches used for?

Answer 14

Ordered lists

Question 15

How does a binary search algorithm work?

Answer 15

1) find the middle item in the ordered list
2) if this is the item you’re looking for, then stop the search - you’ve found it
3) if not, compare the item you’re looking for to the middle item. If it comes before the middle item, get rid of the second half of the list. If it comes after the middle item, get rid of the first half of the list
4) you’ll be left with a list that is half the size of the original list. Repeat steps 1 to 3 on the smaller list to get an even smaller one. Keep going until you find the item you’re looking for

Question 16

What type of lists are linear searches used for?

Answer 16

1) ordered lists

2) unordered lists

Question 17

How does a linear search work?

Answer 17

A linear search checks each item of the list in turn to see if it’s the correct one. It stops when it either finds the item it’s looking for, or has checked every item

Question 18

What is the bubble sort algorithm used for?

Answer 18

To sort an unordered list of items

Question 19

How does a bubble sort algorithm work?

Answer 19

1) look at the first two items in the list
2) if they’re in the right order, you don’t have to do anything. If they’re in the wrong order, swap them
3) move on to the next pair of items (the 2nd and 3rd entries) and repeat step 2
4) repeat step 3 until you get to the end of the list - this is called one pass. The last item will now be in the correct place, so don’t include it in the pass
5) repeat steps 1 to 4 until there are no swaps in a pass

Question 20

What are the advantages of the bubble sort algorithm?

Answer 20

1) it’s a simple algorithm that can be easily implemented on a computer
2) it’s an efficient way to check if a list is already in order
3) doesn’t use much memory as all the sorting is done using the original list

Question 21

What are the disadvantages of the bubble sort algorithm?

Answer 21

1) it’s an inefficient way to sort a list

2) due to being inefficient, the bubble sort algorithm is pretty slow for very large lists of items

Question 22

How does the merge sort algorithm work?

Answer 22

1) split the list in half (the smaller lists are called sub-lists) - the second sub-list should start at the middle item
2) keep repeating step 1 on each sub-list until all the lists only contain one item
3) merge pairs of sub-lists so that each sub-list has twice as many items. Each time you merge sub-lists, sort the items into the right order
4) repeat step 3 until you’ve merged all the sub-lists together

Question 23

What are the advantages of the merge sort algorithm?

Answer 23

1) it’s much more efficient and quicker than the bubble sort algorithm for large lists, and has a similar running time for short lists
2) it has a very consistent running time regardless of how ordered the items in the original list are

Question 24

What are the disadvantages of the merge sort algorithm?

Answer 24

1) even if the list is already sorted it still goes through the whole splitting and merging process, so a bubble sort may be quicker in some cases
2) it uses more memory than the bubble sort because it has to create additional lists