O-LevelComputer ScienceAlgorithm design and problem-solving2210/21 · May/June 2022 · Q57 Marks
The pseudocode represents an algorithm. The pre-defined function DIV gives the value of the result of integer division. For example, Y = 9 DIV 4 gives the value Y = 2 The pre-defined function MOD gives the value of the remainder of integer division. For example, R = 9 MOD 4 gives the value R = 1 First ← 0 Last ← 0 INPUT Limit FOR Counter ← 1 TO Limit INPUT Value IF Value >= 100 THEN IF Value < 1000 THEN First ← Value DIV 100 Last ← Value MOD 10 IF First = Last THEN OUTPUT Value ENDIF ENDIF ENDIF NEXT Counter
- (a)Complete the trace table for the algorithm using this input data: 8, 66, 606, 6226, 8448, 642, 747, 77, 121[5]
- (b)Describe the purpose of the algorithm.[2]
Mark scheme
Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.
- [5] One mark per mark point, max five
- MP1 correct Counter and Limit columns
- MP2 correct Value column
- MP3 correct First column
- MP4 correct Last column
- MP5 correct OUTPUT
- Counter Value First Last Limit OUTPUT
- 0 0 8
- 1 66
- 2 606 6 6 606
- 3 6226
- 4 8448
- 5 642 6 2
- 6 747 7 7 747
- 7 77
- 8 121 1 1 121
- [2] One mark per mark point, max two
- checks for / outputs 3-digit numbers
- where the first and last digit are the same
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