All possible string combinations

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--BlueTaslem's version


-- Returns a list of strings (each of length k)
-- (Works inductively)
function kstrings(chars, k)
    if (k == 0) then -- There is only one length 0 string:
        return {""};
    end

    local function vfind(t,v)
        for i,v1 in next, t do if v1 == v then return v1; end; end;
    end;

    local kminus1s = kstrings(chars, k-1); -- all (k-1)-strings
    local result = {};
    for i = 1, #chars do
        -- chars[i] followed by each (k-1)-string
        for _,km1 in pairs(kminus1s) do
            if (not vfind(result,chars:sub(i, i)..km1)) then
                table.insert(result,chars:sub(i, i)..km1);
            end;
        end;
    end;
    return result;
end;