leetCode No.134 Gas Station
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题目
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.
标签:Greedy
题意
有n个加油站形成了一个环。每个加油站都有gas[i]数量的汽油,汽车加油站i移动到加油站i+1需要汽油cost[i]。现给定gas和cost数组,求是否存在一个加油站的位置,可以让一辆一开始没有油的汽车走完所有加油站。
解题思路
汽车到达一个站会获得gas[i]数量的汽油,前往下一站(i+1站)会消耗cost[i]的汽油,对车的汽油数一直记录,若当前汽车的油量已经为负数说明已经不能继续进行,这时将累计的汽油数清零,从下一个车站开始记录。需要注意的是这样的算法不能判断问题是否有可行解,这样就需要在最开始的时候定义一个total,每次汽车前进都用total = gas[i] - cost[i]来累计total的量。当最后total > 0则有可行解,反之则无。
代码
class Solution(object): def canCompleteCircuit(self, gas, cost): """ :type gas: List[int] :type cost: List[int] :rtype: int """ total = 0 start = 0 m_sum = 0 for i in range(len(gas)): total += gas[i] - cost[i] if m_sum < 0: start = i m_sum = gas[i] - cost[i] else: m_sum += gas[i] - cost[i] if total < 0: return -1 else: return start
相关链接
源代码(github)
原题
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