GATE 2010 CS (CS1) – Question 48

Compiler Design · Parsing and Syntax Analysis · 2 marks · Multiple choice

For the grammar S→aSa | bSb | c, which classification holds?

LL(1) but not LR(1)
LR(1) but not LL(1)
Both LL(1) and LR(1)
Neither LL(1) nor LR(1)

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Correct answer: (C) Both LL(1) and LR(1)

Explanation

The three alternatives have pairwise disjoint FIRST sets {a},{b},{c}; there are no ε-productions. One lookahead token uniquely selects the production, so the grammar is LL(1). Every LL(1) grammar is LR(1), hence C.

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