Asked me couple questions on Leader ship principles on Customer obsession. One Coding challenge

/* Assume input is a source file consisting of two sections. The first section describes

• a "network topology", with each line representing two locations and a cost for interaction
• between these locations. This section begins with the keyword "topology". Assume relations
• are symmetric. A sample follows:
• topology
• a, b, 32
• b, c, 64
• a, c, 16
• b, d, 80
• The second section of the file consists of inquiries requesting the best path between
• locations. This section begins with the keyword "inquiries". A sample follows:
• inquiries
• c, a
• a, d
• The response to the inquiries is path and cost, as in:
• c->a: 16
• a->b->d: 112
• Note that we do not offer the path:
• a->c->b->d: 160
• For your assignment, assume the input file has been read and parsed into the data structures
• of your choosing. Discuss your algorithm design and provide an implementation to answer each
• of the inquiries. Use the language of your choice.
  */

Couldn't complete the challenge. Interviewer respected my honesty and move me to Phone screen. not sure what that means. Help solving this problem is appreciated