O-LevelComputer ScienceAlgorithm design and problem-solving2210/22 · Oct/Nov 2024 · Q48 Marks

This pseudocode algorithm is intended to sort a pre-populated one-dimensional (1D) array named ItemList into alphabetical order using a bubble sort. 01 DECLARE ItemList : ARRAY[1:100] OF STRING 02 DECLARE Counter : STRING 03 DECLARE Limit : INTEGER 04 DECLARE Pass : INTEGER 05 DECLARE Swapped : BOOLEAN 06 DECLARE Temp : STRING 07 Limit ← 100 08 Pass ← 1 09 Temp ← TRUE 10 WHILE Swapped = TRUE OR Pass <= Limit - 1 DO 11 Swapped ← FALSE 12 FOR Counter ← 1 TO Limit - Pass 13 IF ItemList[Counter] > ItemList[Counter + 1] 14 THEN 15 Temp ← ItemList[Counter] 16 ItemList[Counter] ← ItemList[Counter + 1] 17 ItemList[Counter + 1] ← Temp 18 Swapped ← TRUE 19 ENDCASE 20 Pass ← Pass + 1 21 NEXT Counter 22 ENDWHILE

(a)Identify the line numbers of five errors in the pseudocode and suggest a correction for each error. Error 1 line number Correction Error 2 line number Correction Error 3 line number Correction Error 4 line number Correction Error 5 line number Correction[5]
(b)A bubble sort algorithm can be written to include features that make it more efficient. Explain why the corrected bubble sort algorithm is efficient.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[1] Line 02/DECLARE Counter : STRING should be DECLARE Counter : INTEGER
[1] Line 09/Temp ← TRUE should be Swapped ← TRUE
[1] Line 10/WHILE Swapped = TRUE OR Pass <= Limit - 1 DO should be WHILE Swapped = TRUE AND Pass <= Limit - 1 DO
[1] Line 17/ItemList[Counter] ← Temp should be ItemList[Counter + 1] ← Temp
[1] Line 19/ENDCASE should be ENDIF
[1] The use of a flag (set initially to FALSE) to show if a swap has been made (during the current iteration)
[1] to stop the loop if it has been sorted
[1] The reduction in the limit of the (inner) loop after each iteration (of the loop)
[1] to reduce the number of comparisons / iterations required

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