RVHS 2025 H2 Computing Prelim Paper 1

1 9569/01/Prelim/2025 RIVER VALLEY HIGH SCHOOL General Certificate of Education Advanced Level Higher 2 J2 Prelim COMPUTING Paper 1 9569/01 17 Sep 2025 3 hours READ THESE INSTRUCTIONS FIRST Write your center number, index number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, glue or correction fluid. Answer all questions. Approved calculators are allowed. The number of marks is given in brackets [ ] at the end of each question or part question. The total number of marks for this paper is 100. This document consists of 9 printed pages. Answer all questions.

2 9569/01/Prelim/2025 Answer all questions. 1. In the HSG restaurant, dinners are served different types of food based on their appearance. • Soup is served only if diner has short hair. • All diners are served with steak. If diner wears spectacle and has short hair, gold plated steak is served. • If dinner is female and has long hair, the chef will cut the steak for you. Draw a reduced decision table for the above scenario. [6] 2. The following pseudocode performs an operation on a Binary Search Tree (BST). The parameter root refers to the root node of the BST, and Stack is a dynamic data structure implemented using linked nodes. 01 FUNCTION foo(root): 02 stack ← Stack() 03 current ← root 04 05 WHILE current <> NULL OR NOT stack.isEmpty(): 06 WHILE current <> NULL: 07 stack.push(current) 08 current ← current.left 09 10 current ← stack.pop() 11 OUTPUT current.data 12 current ← current.right 13 14 END FUNCTION a) Draw a flow chart for the pseudocode above. [5] b) State the purpose of foo(root). [1] c) Identify the exact line where dynamic memory allocation occurs. [1] A BST with root as the root of the tree is as follows. d) Draw a trace table to trace the current, stack and the OUTPUT when foo(root) is called. [4] 4 3 9 7

3 9569/01/Prelim/2025 e) The following numbers are inserted in the above BST in the same order as shown below: 20, 15, 6, 25 Draw the BST after these numbers are inserted. [2] f) State the pre-order and post-order of the BST. [2] 3. Study the recursive function below. def foo(n, m): if n == 0: return 0 else: return m + foo(n-1, m-2) a) An example of a trace tree diagram showing the recursive function call foo(2,6) is shown as follows: return 10 foo(2,6) return 6 + 4 = 10 foo(1,4) return 4 + 0 = 4 foo(0,2) Use the above example to create a trace tree diagram for the recursive function call foo(4,2) . [3] b) Write in pseudocode the iterative version of foo(n, m). [3]

4 9569/01/Prelim/2025 4. In a real-time online car racing game, once a player completes a round, the time taken is sent to the server for ranking purposes. a) Explain why the finishing time records received by the server may not always arrive in strictly increasing order. [1] The server needs to maintain these records in a data structure where search operations based on finishing time are performed very frequently. b) State the advantage of using a sorted array over a sorted linked list in this context. Support your answer with reference to time complexity. [2] c) State one disadvantage of using a sorted array over a sorted linked list in this context. [1] In this racing game, the finishing times are generally increasing as players complete their rounds one after another. d) Explain why this makes a sorted array particularly efficient for insertion in this context. [2] It was later discovered that some finishing time records are being altered during transmission, either accidentally or maliciously. The server must be able to detect such tampering and ensure that each record truly originates from the legitimate player. e) Suggest a method the server can use to verify the authenticity and integrity of each message. [1] f) Explain how this method works. [6] 5. Hash tables are often described as providing constant-time O(1), search performance. a) State three different reasons why in practical, a hash table cannot always maintain O(1) search time. [3] b) Explain what is meant by collision resolution. [1] c) For each of the following situations, state whether open addressing or closed addressing is the preferred collision resolution strategy. i. When the load factor may be greater than 1. ii. When memory is very limited and space efficiency is important. [1]

5 9569/01/Prelim/2025 6. A company provides an online registration form for customers. The form is shown below. ------------------------------------------------------ | ABC Services - New Customer Registration | |----------------------------------------------------| | Full Name: [________________________] | | Date of Birth (DD/MM/YYYY): [__________] | | Email Address: [________________________] | | Confirm Email Address: [________________________] | | Contact Number: [________________________] | | | | [ Submit ] | ------------------------------------------------------ a) Define data validation and data verification in the context of data entry. [2] b) Suggest one validation check that could be applied to the field Date of Birth. [1] The form asks the user to enter the email address twice (“Email Address” and “Confirm Email Address”). c) Explain the purpose of asking the user to enter the email twice. [2] A customer attempts to enter their Full Name using non-English characters and the system rejects it as it only supports ASCII characters. d) Suggest what the company should do to allow names from different languages to be accepted. [1] Under the Personal Data Protection Act (PDPA), the company has legal obligations when collecting customer personal data through this form. e) State two responsibilities the company must fulfil to comply with PDPA. [2]

6 9569/01/Prelim/2025 7. Answer all the questions. a) You are the network engineer of a company. For each of the following scenarios: • Identify which layer of the TCP/IP model is most directly involved. • Suggest what you would check to troubleshoot the issue. Scenarios: i. Users can connect to the Internet but cannot load the company’s website in their browser. ii. A computer cannot even reach other machines on the same LAN, and pinging local devices fails. iii. The database server is running. Its IP address is reachable. However, client sessions to the database cannot be established and often time out, so applications cannot connect. iv. A user can connect to the local network but cannot reach external networks. [8] b) State two differences between TCP and UDP. [2] Company Z, a healthcare provider, has a central database storing patient records. One employee, John, receives an email with an attachment claiming to be an urgent invoice from a medical supplier. The attachment is actually malicious software that exploits outdated software on John’s computer. When John opens the file, the malware quickly spreads through the network and encrypts the company’s database, making patient records inaccessible. c) Identify the human mistake that allowed the attacker to carry out the attack. [1] d) Name the type of malware that encrypted