GATE | GATE CS 2020 | Question 34

Consider the following grammar.

S → aSB ∣ d
B → b 

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

Note – This question was Numerical Type.
(A) 6
(B) 7
(C) 8
(D) 4

Answer: (B)
Explanation: According to Bottom Up or Shift Reduce Parsers:

Initially: aaadbbb

1. aaaSbbb  {S→d}
2. aaaSBbb  {B→b}
3. aaSbb  {S→aSB}
4. aaSBb  {B→b}
5. aSb  {S→aSB}
6. aSB  {B→b}
7. S  {S→aSB} 

Therefore, total 7 steps required.

Option (B) is correct.

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