A-LevelComputer ScienceData types and structures9618/33 · Oct/Nov 2023 · Q99 Marks

Write the infix expression for this Reverse Polish Notation (RPN) expression: 52 - 5 4 + * 9 /

(a)(i)Write the infix expression for this Reverse Polish Notation (RPN) expression: 52 - 5 4 + * 9 /[2]
(a)(ii)Show how the contents of the following stack will change as the RPN expression in part (a)(i) is evaluated.[4]
(b)Explain how a stack can be used to evaluate RPN expressions.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] (5 – 2)
[1] * (5 + 4) / 9
[2] Final correct expression (5 – 2) * (5 + 4) / 9
[1] One mark per ring (Max 4) First circle: 3 Second circle: 9 Third circle: 27 Fourth circle: 3
[1] MP1 Evaluate the RPN expression from left to right
[1] MP2 Push each element of the RPN expression onto the stack in order until an operator is reached
[1] MP3 Pop the last two elements from the stack and apply the operator
[1] MP4 Push the result of the operation onto the stack
[1] MP5 Repeat the process until the whole expression is evaluated.

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