There seems to be a mistake in the answers to Q 4 in HW 4. I don't get why is it enough to build a graph only with the gas stations, s and t. I think this is a counter example : L=10, V= {s,1,2,t} where only 2 has a station, E = {(s,1),(1,t),(s,2),(2,t)},l(s,1)=2,l(1,t)=3,l(s,2)=10,l(2,t)=10. The shortest path is 5 but the solution will give us 20. Can you tell me if I am wrong or fix the solution if not? Thanks.

HW 4 Q 4 answers