require "table2"
local fmt = require "fmt"

local function ncs(a)
    local f = "%d "
    if type(a[1]) == "string" then
        for i = 1, #a do a[i] = a[i]:byte(1) end
        f = "%c "
    end

    local function generate(m, k, c)
        if k == m then
            if c[m] != c[1] + m - 1 then
                for i = 1, m do fmt.write(f, a[c[i]]) end
                print()
            end
        else
            for j = 1, #a do
                if k == 0 or j > c[k] then
                    c[k + 1] = j
                    generate(m, k + 1, c)
                end
            end
        end
    end

    for m = 2, #a - 1 do
        local c = table.rep(m, 0)
        generate(m, 0, c)
    end
end

local a = {1, 2, 3, 4}
ncs(a)
print()
local ca = {"a", "b", "c", "d", "e"}
ncs(ca)