GATE CSE 2020 Q34: Reduction steps of a bottom-up parse of aaadbbb

Consider the following grammar.

$S \to aSB \mid d$ $B \to b$

The number of reduction steps taken by a bottom-up parser while accepting the string $aaadbbb$ is _______.

Try it: numerical answer: type the value

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Numerical answer. No negative marking.

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Answer: 7 (official GATE 2020 final answer key)

Concept used: Each reduction in a bottom-up parse corresponds to one production used in the rightmost derivation.

First step: Write the derivation of $aaadbbb$ : count the uses of $S \to aSB$ , $S \to d$ and $B \to b$ .

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Source: official GATE 2020 CS question paper and final answer key, organised by IIT Delhi. Question paper · Answer key