Find a starting station that completes the circuit given fuel and travel costs, or return -1.
A good solution should
- State the invariant or decision rule that makes the approach correct.
- Explain time and space costs in terms of input size and required output.
- Handle empty, minimal, duplicate, and boundary-shaped inputs.
Reasoning prompt
If total fuel is insufficient, no solution exists. When a candidate fails, prove why every station in that segment can be skipped.
Use the linked judge for the canonical challenge. The examples above are compact TRT checks; create additional tests around the boundary most likely to break your invariant.