-1.-1 weighted edges to assign them a weight of 1.-1 weighted edges set to 1.
b. Run SPFA from the source and store distances in d1.
c. If the distance to the destination equals the target, finalize the edge weights and return the result.
d. If the distance is less than the target, run SPFA from the destination and store distances in d2.
e. Check if setting any of the remaining -1 weighted edges can make the distance equal to the target.