OpenEuphoria

Re[4]: How to make routine like this

• Posted by aku at inbox.as Dec 14, 2001
• 843 views

I think this is wrong...

I get 151200 for ? get_permutation( digits, 5, 0 )

but I can't repair the problem ( I don't understand. )

Can you correct that? Thanks!

e> Warning! Untested:

e> function get_permutation(sequence symbolSet, integer len, integer
e> permutation)
e>     sequence remaining, out
e>     integer max, pos, divisor, element
e>     integer setLength

e>     setLength = length(symbolSet)

e>     -- Calculate total mumber of permutations and generate an index list
e>     max = 1
e>     remaining = repeat(0, setLength)
e>     for i = 1 to setLength
e>         remaining[i] = i
e>         if i >= len then
e>             max *= i
e>         end if
e>     end for

e>     -- Actions based on permutation number
e>     if permutation = 0 then
e>         -- Handy for calculating exactly how many permutations there are
e>         return max
e>     elsif not (1 <= permutation and permutation <= max) then
e>         -- There are no permutations outside the 1..max range
e>         return -1
e>     end if

e>     -- Generate the output using some cunning math(s)
e>     out = {}
e>     pos = permutation
e>     divisor = max

e>     for i = 1 to len do
e>         divisor /= len - i + 1
e>         element = floor(pos / divisor)
e>         pos -= divisor * element
e>         element += 1
e>         out &= symbolSet[remaining[element]]
e>         remaining =
e>             remaining[1..element-1] &
e>             remaining[element+1..length(remaining)]
e>     end for
e>     return out
e> end function

e> sequence digits
e> digits = {0,1,2,3,4,5,6,7,8,9}

e> ? get_permutation( digits, 5, 0 )
e> -- prints the number of permutations of 'digits' with 5 elements.
e> -- (should be 30240)

e> ? get_permutation( digits, 5, 50000 )
e> -- prints -1 -- there is no 50000th 5-digit permutation of 'digits'.

e> ? get_permutation( digits, 5, 29050 )
e> -- prints the 29050th 5-digit permutation of 'digits'

e> To generate all possible combinations like last time:

e> for i = 1 to get_permutation( digits, 5, 0 ) do
e>     ? get_permutation( digits, 5, i )
e> end for

e> HTH,
e> Carl