Instructions • Type the information required on the front of your Electronic Answer Document. • Before the start of the examination make sure your Centre Number, Candidate Name and Candidate Number are shown clearly in the footer of every page (also at the top of the front cover) of your Electronic Answer Document. • Enter your answers into the Electronic Answer Document. • Answer all questions. • Save your work at regular intervals. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 100. • No extra time is allowed for printing and collating. • The question paper is divided into four sections. Advice You are advised to allocate time to each section as follows: Section A – 40 minutes; Section B – 20 minutes; Section C – 20 minutes; Section D – 70 minutes. At the end of the examination Tie together all your printed Electronic Answer Document pages and hand them to the Invigilator. Warning It may not be possible to issue a result for this paper if your details are not on every page of your Electronic Answer Document. A-level COMPUTER SCIENCE Paper 1 2 IB/G/Jun24/7517/1 Section A You are advised to spend no longer than 40 minutes on this section. Enter your answers for Section A in your Electronic Answer Document. You must save this document at regular intervals. 0 1 State three advantages of using subroutines. For each advantage, you must explain how the advantage is achieved. [3 marks] 0 2 Circular queues and linear queues are examples of data structures that can be implemented using a fixed-length array. 0 2 . 1 Explain why, when implemented using a fixed-length array, a circular queue is usually considered to be a better choice of data structure than a linear queue. [2 marks] 0 2 . 2 Describe the steps that must be completed to remove (dequeue) an item from a circular queue that has been implemented using a fixed-length array. [5 marks] 0 3 0 3 . 1 Describe the Halting problem. [2 marks] 0 3 . 2 Explain the importance of the Halting problem. [1 mark] 3 IB/G/Jun24/7517/1 Turn over ► 0 4 Figure 1 shows four sets R, S, T and U. Three dots (…) means the remaining members of the set follow the same pattern as the previous members of the set. Figure 1 R = {a, b} S = {a, abb, abbbb, abbbbbb, …} T = {bb, bbbb, bbbbbb, …} U = {c, d, bb, b} 0 4 . 1 What is meant by the cardinality of a set? [1 mark] 0 4 . 2 Explain what is wrong with the statement: ‘The only subsets of R are the sets {a}, {b} and {a, b}’. [1 mark] 0 4 . 3 How many members are there in the set formed by the intersection of R and U? [1 mark] 0 4 . 4 The language defined by a regular expression can be represented as a set. Explain the functionality of the | (vertical bar) metacharacter when it is used in a regular expression. [1 mark] The members of the set V are strings that match the regular expression a?b+ Set W is formed by the union of sets S and T. Set X is formed by the set operation V – W. 0 4 . 5 Write a regular expression that would match with all the members of the set W. [2 marks] 0 4 . 6 Write a regular expression that would match with all the members of the set X. [2 marks]