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 Need Help??

Using the dependency graph I posted earlier, I was able to construct a non-recursive implementation of the Ackermann function. It visits the graph left to right, top to bottom.

use strict; use warnings; use feature qw( say ); sub A { my (\$m, \$n) = @_; # \$A[\$m] holds A(\$m, \$n[\$m]) my (@n, @A); for my \$mi (0..\$m) { \$n[\$mi] = -1; \$A[\$mi] = 1; } for (;;) { ++\$n[0]; \$A[0] = \$n[0] + 1; for my \$mi (1..\$m) { last if \$A[\$mi] != \$n[\$mi-1]; \$A[\$mi] = \$A[\$mi-1]; ++\$n[\$mi]; } return \$A[\$m] if \$n[\$m] == \$n; } } say A(@ARGV);

Maybe you'll have better luck with that.

Some properties:

• It only keeps m+1 Ackermann numbers in memory at once.
• It never calculates the same Ackermann number twice.

m<4 can be special-cased. Known formula exist for A(0,n), A(1,n), A(2,n) and A(3,n).

Update: Cleaned up code a bit.

In reply to Re: Non-recursive Ackermann by ikegami

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