GATE CS 2026 Set 1 Q.28: Parsing and Syntax Analysis (LL and LR)

Which of the following statements is/are true?

LL(1) parser uses backtracking

For a grammar to be LL(1), it must be left-recursive

For a grammar to be LL(1), it must be left-factored

The LL(1) parsers are more powerful than the SLR parsers

Official answer and solution

Solution

Recall the necessary conditions and expressive power of predictive LL(1) top-down parsers.

Option (A) is false: An LL(1) parser is a predictive top-down parser that selects productions deterministically using 1 lookahead symbol without backtracking.
Option (B) is false: A left-recursive grammar can never be LL(1).
Option (C) is true: For a grammar to be LL(1), no two productions for the same non-terminal may share a common non-empty prefix (it must be left-factored), otherwise their FIRST sets would overlap.
Option (D) is false: SLR(1) (bottom-up) parsers are strictly more powerful than LL(1) parsers on unambiguous grammars.

Final answer

Option (C)

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Paper: GATE 2026 Computer Science and Information Technology - Session 1 (CS1)
Question: 28 of 65
Section: Computer Science and Information Technology

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