Hello all! I have never completely understood recursion. I have some understanding of what happens when you have one simple recursive call in a subroutine like the following:
sub factorial
{
factorial
my ($n) = @_;
return 1 if $n == 0;
return factorial($n1) * $n;
}
The sub factorial is called again and again until $n is equal to 0. Then the 1 is returned and all the past calls are then 'really' executed in reverse order, producing the factorial of the number $n.
OK. But I do not understand how recursion works when there is more than 1 recursive call in a subroutine, like the following:
sub hanoi
{
my ($n, $start, $end, $extra) = @_;
if ($n == 1)
{
print "Move disk #1 from $start to $end.\n";
}
else
{
hanoi($n1, $start, $extra, $end);
print "Move disk #$n from $start to $end.\n";
hanoi($n1, $extra, $end, $start);
}
}
The output will be:
Move disk #1 from A to C.
Move disk #2 from A to B.
Move disk #1 from C to B.
Move disk #3 from A to C.
Move disk #1 from B to A.
Move disk #2 from B to C.
Move disk #1 from A to C.
Can anyone explain precisely why this is the output. If the first recursive call were called over and over untill $n==1 and then they 'fell' back and all the calls were executed in reverse order, the third line of output does not make sense. Is the next recursive line then executed?
A stepbystep explanation is what I am looking for.
Thank you!
Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
Read Where should I post X? if you're not absolutely sure you're posting in the right place.
Please read these before you post! —
Posts may use any of the Perl Monks Approved HTML tags:
 a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
Outside of code tags, you may need to use entities for some characters:

For: 

Use: 
 &   & 
 <   < 
 >   > 
 [   [ 
 ]   ] 
Link using PerlMonks shortcuts! What shortcuts can I use for linking?
See Writeup Formatting Tips and other pages linked from there for more info.

