ISRO Computer Science (CSE) 2025 - Question 33

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Topic: Theory of Computation

Which of the following strings will correctly match the Grammar G represented by production rules given?
$S\rightarrow A|B$
$A\rightarrow aAb | c$
$B\rightarrow bBd | e$

  • A. accbb
  • B. aacbb
  • C. abaed
  • D. aaebb

Answer: B. aacbb

Explanation: From the production rules:
$A \rightarrow aAb | c$ generates strings of the form $a^n c b^n$ where $n \ge 0$.
$B \rightarrow bBd | e$ generates strings of the form $b^m e d^m$ where $m \ge 0$.
The language generated by S is the union of these two sets: $\\{a^n c b^n\\} \cup \\{b^m e d^m\\}$.
Checking the options, 'aacbb' matches the pattern $a^n c b^n$ with $n=2$ ($a^2 c b^2$). The other options do not match either pattern.

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