// InverseTransform reverses the bwt to original byte slice
func InverseTransform(t []byte, es byte) []byte {
n := len(t)
lines := make([][]byte, n)
for i := 0; i < n; i++ {
lines[i] = make([]byte, n)
}
for i := 0; i < n; i++ {
for j := 0; j < n; j++ {
lines[j][n-1-i] = t[j]
}
sort.Sort(byteutil.SliceOfByteSlice(lines))
}
s := make([]byte, n-1)
for _, line := range lines {
if line[n-1] == es {
s = line[0 : n-1]
break
}
}
return s
}
// 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
}
