permute_string: returns a table of all permutations of `str`

permute_string.lua

--- returns a table of all permutations of `str`
local function permute_string( str )
    local string_byte, string_char = string.byte, string.char

    local src = {}
    for i = 1, #str do 
        src[i] = string_byte( str, i )
    end

    local perm = {}
    local permute_fn
    permute_fn = function( a, n )
        if n == 0 then
            perm[string_char(unpack(a))] = true
        else
            for i = 1, n do
                a[i], a[n] = a[n], a[i]
                permute_fn( a, n - 1 )
                a[i], a[n] = a[n], a[i]
            end
        end
    end

    permute_fn( src, #src )

    local ret = {}
    for k, _ in pairs(perm) do
        ret[#ret+1] = k
    end
    return ret
end