SQL & PL/SQL :: Get All Possible Paths?

Suppose I have 4 Inputs 'A','B','C' and 'D'.

Problem is I have to get all the path from
1st 'A''B''C''D' to 'A'
2nd 'A''B''C''D' to 'B'
3rd 'A''B''C''D' to 'C'
4th 'A''B''C''D' to 'D'

For 1st one all the possible paths will be:

ABCD --> ABC --> AB --> A
ABCD --> ABC --> AC --> A
ABCD --> ABD --> AB --> A
ABCD --> ABD --> AD --> A
ABCD --> ACD --> AC --> A
ABCD --> ACD --> AD --> A
... same approach for second path and so on...

The inputs may vary in number, like they may be 'A','B','C','D','E'... so on.

Note: This may not seems to be a Oracle problem, but I have to do it in Oracle as my further steps will depend on this.