134. Gas Station

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        i           j

• conclusion: Assume that i can reach j at the farthest. We should consider j+1 next time.

Why do the stations between i and j no longer need to be considered?

Let's illustrate this using proof by contradiction.

Assume that i+1 meets the requirements and it can complete a circle.
At first wo move from i to i+1, and then from i+1 to j+1 So we can reach j+1 from i.
But i only can reach j. There's contradiction and the proof is complete.