local fmt = require "fmt"
require "table2"

local function encode(s)
    if s == "" then return {} end
    local symbols = "abcdefghijklmnopqrstuvwxyz":split("")
    local result = table.rep(#s, 0)
    for i = 1, #s do
        local c = s[i]
        local index = symbols:findindex(|ch| -> ch == c)
        if !index then error($"{s} contains a non-alphabetic character") end
        result[i] = index
        if index > 1 then
            for k = index - 1, 1, -1 do symbols[k + 1] = symbols[k] end
            symbols[1] = c
        end
    end
    return result
end

local function decode(a)
    if #a == 0 then return "" end
    local symbols = "abcdefghijklmnopqrstuvwxyz":split("")
    local result = table.rep(#a, "")
    local i = 1
    for a as n do
        if n < 1 or n > 26 then error($"{fmt.format("%,s", a)} contains an invalid number") end
        result[i] = symbols[n]
        if n > 1  then
            for j = n - 1, 1, -1 do symbols[j + 1] = symbols[j] end
            symbols[1] = result[i]
        end
        i += 1
    end
    return result:concat("")
end

local strings = {"broood", "bananaaa", "hiphophiphop"}
local encoded = table.create(#strings)

for i, s in strings do
    encoded[i] = encode(s)
    fmt.print("%-12s -> %,s", s, encoded[i])
end
print()
local decoded = table.create(#encoded)
i = 1
for encoded as a do
    decoded[i] = decode(a)
    local correct = (decoded[i] == strings[i]) ? "correct" : "incorrect"
    fmt.print("%,-38s -> %-12s -> %s", a, decoded[i], correct)
    i += 1
end