Problem with a matrix

I have a scattered matrix that I have to import from an external file. In
this case all the lines could have a different size. The graph is oriented.
I give you an example:
a b c
b a c d
c b

The first row expresses that "a" has a direct path with "b" and also with
"c".
In the second "b" has a path with "a" and one with "c". In the third "c"
there is a direct path with "b".
I want to obtain the adjacency matrix.  In this case it is:
0 1 1 0
1 0 1 1
0 1 0 0
0 0 0 0

What have I to do?
Please help me. Excuse me for my english.
Alessandro Ambrosini

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