// Transform return Burrows-Wheeler-Transform of s
func (fmi *FMIndex) Transform(s []byte) ([]byte, error) {
bwt, rotations, err := bwt.Transform(s, fmi.EndSymbol)
if err != nil {
return nil, err
}
fmi.BWT = bwt
fmi.M = rotations
fmi.CountOfLetters = byteutil.CountOfByte(fmi.BWT)
fmi.Alphabet = byteutil.AlphabetFromCountOfByte(fmi.CountOfLetters)
fmi.C = ComputeC(fmi.M, fmi.Alphabet)
fmi.Occ = ComputeOccurrence(fmi.BWT, fmi.Alphabet)
return bwt, nil
}
// Transform returns Burrows–Wheeler transform of a byte slice.
// See https://en.wikipedia.org/wiki/Burrows%E2%80%93Wheeler_transform
func Transform(s []byte, es byte) ([]byte, [][]byte, error) {
count := byteutil.CountOfByte(s)
if _, ok := count[es]; ok {
return nil, nil, ErrEndSymbolExisted
}
s = append(s, es)
n := len(s)
rotations := make([][]byte, n)
i := 0
for j := 0; j < n; j++ {
rotations[i] = append(s[n-j:], s[0:n-j]...)
i++
}
sort.Sort(byteutil.SliceOfByteSlice(rotations))
bwt := make([]byte, n)
i = 0
for _, t := range rotations {
bwt[i] = t[n-1]
i++
}
return bwt, rotations, nil
}
