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Re: Zeckendorf representation

by jwkrahn (Monsignor)
on Aug 25, 2012 at 02:58 UTC ( #989681=note: print w/ replies, xml ) Need Help??


in reply to Zeckendorf representation

sub is_fibonnacci { my $plus = (5 * $_[0] * $_[0]) + 4; my $mins = (5 * $_[0] * $_[0]) - 4; return is_perfect_square($plus) | is_perfect_square($mins); }

No need to calculate 5 * $_[0] * $_[0] twice, and you probably meant to use the logical or operator instead of the bit-wise or operator.

sub is_fibonnacci { my $plus = (5 * $_[0] * $_[0]) + 4; my $mins = $plus - 8; return is_perfect_square($plus) || is_perfect_square($mins); }

(The logical operators short-circuit so is_perfect_square($mins) will only execute if is_perfect_square($plus) is true.)



sub is_perfect_square { my $sqrt = int(sqrt($_[0])); return $sqrt * $sqrt == $_[0]; }

Or just:

sub is_perfect_square { int( $_[0] ** .5 ) ** 2 == $_[0] }


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Re^2: Zeckendorf representation
by thmsdrew (Scribe) on Aug 25, 2012 at 03:11 UTC

    Thanks for your input! What do you mean by "short circuit"? Also, the difference between your is_perfect_square sub and mine is that mine is much more clear. I can afford the extra line for a bit of clarity.

      What do you mean by "short circuit"?
      It means that the part after || will only be evaluated if it is needed know the result of the operator. In the case of the or-operator the second half is redundant if the first is true, since the total will be true no matter what the second part is.

        I don't really understand how that is a problem. If the first part passes, then I want it to return true, and I truly don't care what the second part is. I guess I see how that's redundant, though.

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