187. 加油站

class Solution:
    """
    @param gas: An array of integers
    @param cost: An array of integers
    @return: An integer
    """
    ‘‘‘
    大致思路:
    1.给出total 汽油量，如果汽油量小于0的话，则当前位置index+1，并且重置汽油量.直到最后一直符合的即跳出
    ‘‘‘
    def canCompleteCircuit(self, gas, cost):
        if sum(gas) < sum(cost):
            return -1
        
        total = 0
        j = 0 
        for i in range(len(gas)):
            total = total + gas[i] - cost[i]
            if total < 0:
                total = 0
                j = i + 1
        return j