Compiler design Self doubt

Question

1. S → aSbS /bSaS / ϵ

2. S → aABb 

           A→ c/ ϵ

           B → d/ ϵ

Which of the following is LL1. Explain in details.

Comments

both in LL1

LL1 only checks FIRST of grammar and if there same alphabet or not.

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But it is mentioned that 1 is not LL1

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yes, thanks for correcting

Answer 1

$1)$ $FT(S)=\left \{ a,b,\epsilon \right \}$

$FL(S)=${ a,b,$}

NonTerminal
	a	b	$
S	$S->aSbS$. ,  $S->\epsilon $	$S->bSaS$. ,  $S->\epsilon $	$S->\epsilon $

 

yes it is not $LL(1).$

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$2)$ $FT(S)=\left \{ a \right \}$

$FT(A)=\left \{ c,\epsilon \right \}$

$FT(B)=\left \{ d,\epsilon \right \}$

$FL(S)=${$}

$FL(A)=${d,b}

$FL(B)=${b}

NonTerminal
	a	b	c	d	$
$S$	$S->aABb$
$A$		$A\rightarrow \epsilon$	$A\rightarrow c$	$A\rightarrow \epsilon$
$B$		$B\rightarrow \epsilon$		$B->d$

 

It is $LL(1).$

Comments

Thanks.. :)