How do optimizers/minifiers work and what's the difference?

Question

Programming

How from this one (abstract PL):

Hex C = "#000";  // "мысли" минификатора: значение не используется и обязательно изменится => пропускаем
int R = random(1, 3);  // R - число от 1 до 3
if (R == 1) C = "#111"
if (R == 2) C = "#222"
if (R == 3) C = "#333" // замечена какая-то закономерность => превращаем в массив

do this

Hex C = "#" + Array('111', '222', '333') [random(0, 2)]

?
Are there any code shorteners without loss of readability, such as turning noobish scripts into at least partially normal code? The question arose while rewriting my old code.
And how do such tools work from the inside?