The files containing the instances have the following format:
u1 u2 cost req
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u1 u2 cost
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!********************************************************************
- r represents the number of depots
- d1 d2 ... dr are the indices of the nodes where depots are located.
- For each edge connecting nodes u1 and u2 there is a line:
u1 u2 cost req
where req is equal to 1 if it is a required edges and 0 otherwise