aoc-day6-faster.go

func blockPosition(datastream []byte, size int) (int, error) {
        block := make([]byte, size)
        start := 0
        count := 1
        var duplicateIndex int
        for i := 1; i < len(datastream); {
                block = datastream[start : start+count]
                if count == size {
                        return i, nil
                }
                duplicateIndex = bytes.IndexByte(block, datastream[i])
                if duplicateIndex == -1 {
                        count += 1
                } else {
                        count = count - duplicateIndex
                        start = start + duplicateIndex + 1
                }
                i += 1
        }

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