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Subjects · Leaving Cert Computer Science

Leaving Cert Computer Science: Searching algorithms

How often Searching algorithms comes up on the Computer Science papers, every year it was asked, and questions to try.

HL Asked on 2 of the last 5 Higher Level papers, most recently in 2025.

OL Asked on 4 of the last 5 Ordinary Level papers, most recently in 2024. most years

Searching algorithms, Higher Level(8 marks)

Quick ones on Searching algorithms.

(a)What must be true of a list before a binary search can be used on it?
  1. It must hold only numbers
  2. It must be sorted
  3. It must have an even length
(b)What is the maximum number of comparisons a binary search needs for 31 sorted items?
  1. 16
  2. 31
  3. 5
(c)A linear search looks for a value that is not in a list of 50 items. How many comparisons?
  1. 50
  2. 1
  3. 25
Show the answers

(a) It must be sorted

(b) 5

(c) 50

Your turn: Higher Level questions on Searching algorithms.

Higher Level

Asked on 2 of the last 5 Higher Level papers, most recently in 2025.

Every paper, year by year

YearWhere it came up
2025A7
2024Not asked
2023B15
2022Not asked
2021Not asked

Links open the State Examinations Commission’s paper for that year.

More Searching algorithms questions

Searching algorithms, 2 marks

A linear search finds its target at the 5th position of a list. How many comparisons were made?

  1. 4
  2. 1
  3. 5
Show the answer

5

Linear search checks items one at a time from the start, so reaching the 5th item takes 5 comparisons. 4 is its index, as indexes start at 0.

Searching algorithms, 3 marks

A linear search looks for 12 in a list sorted smallest first. If 12 is missing, when can it stop early?

  1. After checking the middle item of the list
  2. When it reaches an item bigger than 12
  3. Only after checking every item in the list
Show the answer

When it reaches an item bigger than 12

In a sorted list everything after a bigger item is bigger still, so 12 cannot appear later. On an unsorted list it must check every item.

Ordinary Level

Asked on 4 of the last 5 Ordinary Level papers, most recently in 2024. most years

Every paper, year by year

YearWhere it came up
2025Not asked
2024B13
2023A8
2022A5
2021A10, B14

Links open the State Examinations Commission’s paper for that year.

More Searching algorithms questions

Searching algorithms, 2 marks

Binary search only works if the list is…

  1. Short
  2. Made of numbers
  3. Sorted
Show the answer

Sorted

Binary search checks the middle item and throws away the half that can't hold the target. That only works if the items are in order.

Searching algorithms, 2 marks

Linear search checks the items…

  1. Last item only, then stops
  2. One by one from the start
  3. Middle item first, then half
Show the answer

One by one from the start

Linear search works on any list, sorted or not, but can be slow: it may have to check every item.

Searching algorithms, 3 marks

Linear search for 8 in [3, 8, 5, 1]. How many comparisons?

  1. 2
  2. 1
  3. 4
Show the answer

2

Compare with 3: no. Compare with 8: found. 2 comparisons, and the search stops as soon as it finds the target.

Other Computer Science topics

All of Leaving Cert Computer Science