leetcode @python 134. Gas Station

题目链接

https://leetcode.com/problems/gas-station/

题目原文

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.

题目大意

在一条回路上，有n个加油站，每个加油站的油量为gas[i]，从油站i到油站i+1的耗油量为cost[i],给定gas数组和cost数组，返回能够可以环绕这条回路的油站的索引，若不能环绕，则返回-1

解题思路

1. 若总的油量小于总的cost，则肯定不能环绕
2. 假设当前剩余的油量为sumcost，若达到站点i的的剩余油量小于0，则将设置起始站点设为i；另外设置所有站点的剩余油量为total，当total小于0，则不能环绕，否则可以

代码

class Solution(object):
    def canCompleteCircuit(self, gas, cost):
        """
        :type gas: List[int]
        :type cost: List[int]
        :rtype: int
        """
        if sum(gas) < sum(cost):
            return -1

        sumcost = 0
        total = 0
        min_idx = 0

        for i in range(len(gas)):
            total += gas[i] - cost[i] 
            if gas[i] + sumcost < cost[i]:
                min_idx = i + 1
                sumcost = 0
            else:
                sumcost += gas[i] - cost[i]

        if total >= 0:
            return min_idx
        else:
            return -1