local target = "METHINKS IT IS LIKE A WEASEL"
local alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ "
local c, p = 100, 0.06
 
local function fitness(s)
    local score = #target
    for i = 1,#target do
        if s:sub(i,i) == target:sub(i,i) then score = score - 1 end
    end
    return score
end
 
local function mutate(s, rate)
    local result, idx = ""
    for i = 1,#s do
        if math.random() < rate then
            idx = math.random(#alphabet)
            result = result .. alphabet:sub(idx,idx)
        else
            result = result .. s:sub(i,i)
        end
    end
    return result, fitness(result)
end
 
local function randomString(len)
    local result, idx = ""
    for i = 1,len do
        idx = math.random(#alphabet)
        result = result .. alphabet:sub(idx,idx)
    end
    return result
end
 
local function printStep(step, s, fit)
    print(string.format("%04d: ", step) .. s .. " [" .. fit .."]")
end
 
math.randomseed(os.time())
local parent = randomString(#target)
printStep(0, parent, fitness(parent))
 
local step = 0
while parent ~= target do
    local bestFitness, bestChild, child, fitness = #target + 1
    for i = 1,c do
        child, fitness = mutate(parent, p)
        if fitness < bestFitness then bestFitness, bestChild = fitness, child end
    end
    parent, step = bestChild, step + 1
    printStep(step, parent, bestFitness)
end