The input is:

[3, 1, 9, 5, 1, 1, 10]

[5, 6, 2, 3, 4, 8, 3]

And the expected answer is 6

Ok, start at station 6, the car get 10 gas and consume 3 to reach station 0

Then the car has 7 gas at station 0

Go ahead:

at station 0 -> 0 + 10 - 3 = 7

at station 1 -> 7 + 3 - 5 = 5

at station 2 -> 5 + 1 - 6 = 0

at station 3 -> 0 + 9 - 2 = 7

at station 4 -> 7 + 5 - 3 = 9

at station 5 -> 9 + 1 - 4 = 6

We still need to travel to station 6. However, we only have 6(remaining) + 1(this station) = 7 gas and we need to consume 8 to get to station 6. So I think the answer is -1.

Anyone can tell me why the answer is 6 instead of -1?