Re^2: Finding the max()/min()


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Re^2: Finding the max()/min()

by sleepingsquirrel (Chaplain)

on Nov 11, 2004 at 19:47 UTC ( [id://407163]=note: print w/replies, xml )

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in reply to Re: Finding the max()/min()
in thread Finding the max()/min()

Your recursive version of max is broken for lists like (-1,0,1,2) and (-1,undef,1,2). i.e. the code assumes it is at the end of the list whenever $next==0 or $next==undef (which isn't true in general). Here's a snazzy (if not the most efficient) recursive version with a hat tip to Zaxo...

sub max {
    my ($x, @xs) = @_;
    @xs ? ($x, max(@xs))[$x < max(@xs)] : $x
}
[download]

-- All code is 100% tested and functional unless otherwise noted.

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Re^3: Finding the max()/min() by Ven'Tatsu (Deacon) on Nov 11, 2004 at 22:02 UTC
Your solution is calling `max(@xs)` twice each step. This leads to O(2^n) growth for what should be an O(n) problem. Modifying it slightly to call max once and save the value in a temp variable should save considerable time on long lists. `sub max { my ($x, @xs) = @_; @xs ? do { my $m = maxdo(@xs); ($x, $m)[$x < $m] } : $x; }` [download]	[reply] [d/l] [select]

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