Gas stations on a circular route. Station i has gas[i] fuel and costs cost[i] to reach the next station. Find the starting station to complete the circuit, or return if impossible.
Example: gas = [1,2,3,4,5], cost = [3,4,5,1,2]. Start at station (-indexed). Can you complete the circuit? What is the greedy approach? Constraint: . Simulating every start is time using space. Greedy gives .