LeetCode Gas Station
来源:互联网 发布:网络访问控制 编辑:程序博客网 时间:2024/06/07 09:25
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.
思路分析:这题O(n^2)的解法容易想到,可以从零开始,不断试探向后面走,如果发现油量为负数,则改变起点为1,以此类推。但是这种解法会超时。这题有O(n)的解法,也就是采用双指针的思路,用i来标记当前的start point,j表示当前car到达的station,用sum来表示car剩下多少油量,那么从i开始,j是当前station的指针,sum += gas[j] – cost[j] (从j站加了油gas[j],再算上从i开始走到j剩的油sum,减去从j走到j+1的油耗cost[j],这里是试探是否能走到j+1)。如果sum < 0,就说明从i开始是不行的,需要更新start point i。那能不能从i到j中间的某个位置开始呢?假设能从k (i <=k<=j)走,由于sum[i..j] < 0,如果sum[k..j] >=0,说明sum[i..k – 1]<0,那从i开始到k肯定无法到达,也就是说,从k出发,肯定是没有办法回到k的(至少i到k无法走)。所以一旦sum<0,应该把i赋成j + 1,sum归零。最后用total表示能不能走一圈。对于环状数组或者链表,经常可以用双指针的思路得到巧妙的解法,类似的题目还有判断一个链表是否存在circle,也可以用双指针的思路得到O(n)的解法。
这题参考了这个题解,需要更加深入思考反复理解。
AC Code
public class Solution { public int canCompleteCircuit(int[] gas, int[] cost) { int i = 0; int j = 0; int sum = 0; int total = 0; while(j < gas.length){ int leftGas = gas[j] - cost[j]; if(sum + leftGas < 0){ i = j + 1; sum = 0; } else { sum += leftGas; } j++; total += leftGas; } if(total >= 0) return i; else return -1; }};
- LeetCode:Gas Station
- [LeetCode] Gas Station
- [leetcode]Gas Station
- Leetcode: Gas Station
- LeetCode:Gas Station
- [LeetCode] Gas Station
- leetcode Gas Station
- [LeetCode]Gas Station
- LeetCode 之 Gas Station
- leetcode Gas Station
- 【Leetcode】Gas Station
- LeetCode | Gas Station
- LeetCode之Gas Station
- Leetcode: Gas Station
- LeetCode OJ:Gas Station
- [LeetCode]134.Gas Station
- [Leetcode] Gas Station (Java)
- gas station leetcode
- 高通平台底电流调节心得
- C# 复制文件夹
- AutoCompleteTextView自动完成文本框
- 程序员要知道的英语词汇
- Hive的multi-distinct可能带来性能恶化之案例优化
- LeetCode Gas Station
- cocos2dx 3.0 对战的寻路AI
- 解决休眠底电流过大调试步骤
- Lync Server 2010安装准备(三)—— 前端服务器上安装Lync Server 2010
- [NOTES]C++标准IO
- STM32电源管理
- C# 生成自定义长度的0-z随机字符串
- android(Google公司开发的操作系统)
- 文件处理函数