1. WJEC GCSE Computer Science
Unit 2
Searching and Sorting

2. Learning Intentions and Outcomes
Explain and use linear and binary search algorithms.
Describe the characteristics of merge sort and bubble sort algorithms.
Developing
Explain how linear and binary search algorithms work
Follow linear and binary search algorithms to identify if an item is found in a list
Describe how the merge sort algorithm works
Describe how the bubble sort algorithm works
Secure
Demonstrate a bubble sort algorithm on a set of data
Demonstrate a merge sort algorithm on a set of data

3. Linear Search
Linear search is the simplest searching algorithm; it starts at the first element in the list and checks every element until it finds the one it is looking for. LIST = Let’s search for 7: SEARCH = 7 FOR i in range(LIST): if LIST[i] == SEARCH: RETURN “Found” 3 8 1 4 7 6 9 2 12 11 10 5

4. Binary Search
Binary search is a good way of searching lists that have been sorted. At each step it halves the number of items it needs to look at.
In this example we are going to search for 14. 1 2 4 5 6 8 10 12 13 14 15
1 FUNCTION BSearch(List, ItemToFind, Min, Max)
Variable
Value
Min
Max
MidPoint
2 MidPoint = (Min + ((Max – Min / 2)) 6
3 IF List[MidPoint] < ItemToFind THEN
(10-5) 5 9 11
4 Bsearch(List, ItemToFind, MidPoint+1, Max) 10 8 5
5 ELSE IF List[MidPoint] > ItemToFind THEN
Return Value 10
6 Bsearch(List, ItemToFind, Min, MidPoint-1)
7 ELSE
8 RETURN MidPoint
9 END IF
9 END FUNCTION

5. Comparing Linear and Binary Search

6. Bubble Sort

7. Bubble Sort
One “Pass” of the Bubble Sort Algorithm A “Pass” is an iteration over the entire unsorted section of the array.

8. Merge Sort

9. Workbook
Complete section 10 Q1-4