string-compression.go

func Reduce[T any, R any](arr []T, fn func(acc R, val T) R) R {
	var acc R

	for _, v := range arr {
		acc = fn(acc, v)
	}

	return acc
}

type Tuple struct {
	count int
	char  byte
}

func (t *Tuple) ToString() string {
	return fmt.Sprintf("{ count: %d, char: %c }", t.count, t.char)
}

func Compress(str []byte) string {
	compressed := Reduce(str, func(acc []Tuple, val byte) []Tuple {
		var last *Tuple
		if len(acc) == 0 {
			last = &Tuple{}
		} else {
			last = &acc[len(acc)-1]
		}

		if last.char == val {
			last.count++
		} else {
			acc = append(acc, Tuple{1, val})
		}
		return acc
	})

	if len(compressed) > len(str) {
		return string(str)
	}

	return Reduce(compressed, func(acc string, t Tuple) string {
		acc += fmt.Sprintf("%c%d", t.char, t.count)
		return acc
	})
}