aoc-day6-even-faster.go

func blockPosition(datastream []byte, size int) (int, error) {
        start := 0
        count := 1
        indexes := make([]int, 256)
        for i := 0; i < 256; i++ {
                indexes[i] = -1
        }
        var index int
        indexes[datastream[0]] = 0
        var i = 1

        for ; count < size; i++ {
                block := datastream[start : start+count]
                b := datastream[i]

                index = indexes[b]
                if index < 0 {
                        indexes[b] = count
                        count += 1
                } else {
                        for j := 0; j < index; j++ {
                                indexes[block[j]] = -1
                        }
                        for j := index + 1; j < count; j++ {
                                indexes[block[j]] -= index + 1
                        }
                        count = count - index
                        start = start + index + 1
                        indexes[b] = count - 1
                }
        }
        if count == size {
                return i, nil
        }

        return 0, errors.New("not found")
}