[python] Breadth First Search

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I am going to implement breadth first search with Python and data will be
read from a text file where the structure of the file structure as follow

Could you give me any idea how to implement the program?

<total number of nodes>
<first node><second node><distance from first node to second node>
...
<end of file represented by -1>

The aims is to find out the shortest path(s) for the leaf node(s)

Example:
10
0 1 2
0 5 3
1 2 2
1 3 4
2 1 3
2 3 1
5 6 3
5 7 1
6 8 -1
7 8 1
7 9 2
9 5 3
-1

Possible solution:
Path=0,1,2,3 length=5
Path=0,5,6,8 length=5
Path=0,5,7,8 length=5

Thanks a lot!

Nicky.