Question
Each bus route is a fixed list of stops it serves; routes[i] is the list of stops served by bus i. Starting at bus stop source, return the least number of buses you must take to reach bus stop target. You may board any bus whose route includes your current stop and ride it to any other stop on that route. Return 0 if source equals target, and -1 if target is unreachable. There are at most 500 routes.
min_buses(routes: list[list[int]], source: int, target: int) → int[[[1,2,7],[3,6,7]],1,6]out2State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.