Gas Station Leetcode Python

There are N gas stations along a circular route, where the amount of gas at station i is gas[i].


You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an empty tank at one of the gas stations.


Return the starting gas station's index if you can travel around the circuit once, otherwise return -1.


Note:

The solution is guaranteed to be unique.

首先判断总的油够不够consume,如果总的油小于总的消耗那一定是走不完的。其次判断，过程中是否剩的油会小于0，如果小于0 那只能从下一个station开始。遍历一遍即可得到答案。

1. compare total gas and total cost, if             total gas<total cost 

return -1

2. iterate the whole station, rest+=gas[i]-cost[i] if rest<0, search start from the next i

return station

class Solution:
    # @param gas, a list of integers
    # @param cost, a list of integers
    # @return an integer
    def canCompleteCircuit(self, gas, cost):
        if sum(gas)<sum(cost):
            return -1
        else:
            pre=0
            rest=0
            station=0
            for index in range(len(gas)):
                rest+=gas[index]-cost[index]
                if rest<0:
                    pre+=rest
                    rest=0
                    station=index+1
        return station