[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.

具体分析可以参考 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