[Leetcode]Gas Station

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.

具體分析可以參考 http://blog.csdn.net/linhuanmars/article/details/22706553

class Solution:
    # @param gas, a list of integers
    # @param cost, a list of integers
    # @return an integer
    def canCompleteCircuit(self, gas, cost):
        if gas is None or len(gas) == 0 or cost is None or len(cost) == 0 or len(gas) != len(cost):
            return -1
        sumVal = total = 0; index = -1
        for i in xrange(len(gas)):
            sumVal += gas[i] - cost[i]
            total += gas[i] - cost[i]
            if sumVal < 0:
                sumVal = 0
                index = i
        return index + 1 if total >= 0 else -1