Question

Identify the unambiguous grammar.

• A. None of these
• B. $E\to E+E|E\ast E|id$
• C. $S\to aS|Sb|\epsilon$
• D. $S\to |aSb|\epsilon$

Answer 1

The correct option is D $S\to |aSb|\epsilon$

$\left(A\right)E\to E+E|E^{\ast }E|$ id is ambiguous grammar.

"id + id * id" has 2 Parse trees

$\left(B\right)S\to aS|Sb|\epsilon$ is ambiguous grammar.
"ab" has 2 Parse trees

$\left(C\right)S\to aSb|\epsilon$ is unambiguous grammer.
Every string in $a^n{b}^n$ has one Parse tree