Leetcode 134 Gas Station
来源:互联网 发布:webmethod 返回json 编辑:程序博客网 时间:2024/04/30 03:46
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.
求出gas-cost和最小的位置,那么从他的下一个位置开始,必定可以通过。
然后在discuss看到了更好的做法:是否可达和我的一样,但是起始位置和我的想法不一样,
一旦发现和小于0,则把它下一个位置置为起始位置,更新tank为0,最后得到的起始位置就是结果。
因为每发现和小于0,则可以把这些加油站看作一个加油站,一直到最后只有两个两个加油站,后一个加前一个必然大于等于0!
有可能没说清楚,贴上英文原文解释:
Proof to the first point: say there is a point C between A and B -- that is A can reach C but cannot reach B. Since A cannot reach B, the gas collected between A and B is short of the cost. Starting from A, at the time when the car reaches C, it brings in gas >= 0, and the car still cannot reach B. Thus if the car just starts from C, it definitely cannot reach B.
Proof for the second point:
- If there is only one gas station, it’s true.
- If there are two gas stations a and b, and gas(a) cannot afford cost(a), i.e., gas(a) < cost(a), then gas(b) must be greater than cost(b), i.e., gas(b) > cost(b), since gas(a) + gas(b) > cost(a) + cost(b); so there must be a way too.
- If there are three gas stations a, b, and c, where gas(a) < cost(a), i.e., we cannot travel from a to b directly, then:
- either if gas(b) < cost(b), i.e., we cannot travel from b to c directly, then cost(c) > cost(c), so we can start at c and travel to a; since gas(b) < cost(b), gas(c) + gas(a) must be greater than cost(c) + cost(a), so we can continue traveling from a to b. Key Point: this can be considered as there is one station at c’ with gas(c’) = gas(c) + gas(a) and the cost from c’ to b is cost(c’) = cost(c) + cost(a), and the problem reduces to a problem with two stations. This in turn becomes the problem with two stations above.
- or if gas(b) >= cost(b), we can travel from b to c directly. Similar to the case above, this problem can reduce to a problem with two stations b’ and a, where gas(b’) = gas(b) + gas(c) and cost(b’) = cost(b) + cost(c). Since gas(a) < cost(a), gas(b’) must be greater than cost(b’), so it’s solved too.
- For problems with more stations, we can reduce them in a similar way. In fact, as seen above for the example of three stations, the problem of two stations can also reduce to the initial problem with one station.
class Solution {public: int canCompleteCircuit(vector<int>& gas, vector<int>& cost) { int sum = 0, minn = INT_MAX, pos; for(int i = 0;i < gas.size();i++) { sum+=(gas[i]-cost[i]); if(minn > sum) { minn = sum; pos = i; } } if(sum<0) return -1; return (pos+1) % gas.size(); }};
- LeetCode: Gas Station [134]
- LeetCode(134)Gas Station
- [LeetCode 134]Gas Station
- LeetCode 134 Gas Station
- leetcode || 134、Gas Station
- [leetcode] 134 Gas Station
- LeetCode(134) Gas Station
- 【Leetcode】Gas Station #134
- leetcode 134: Gas Station
- Gas Station - LeetCode 134
- 134 Gas Station [Leetcode]
- Leetcode #134 Gas Station
- LeetCode 134 Gas Station
- LeetCode 134 - gas station
- LeetCode 134 Gas Station
- LeetCode 134 Gas Station
- Leetcode 134 Gas Station
- LeetCode(134) Gas Station
- 怎么导入从github上下载下来的android studio项目
- 函数
- 一天一条Linux指令-命令总目录
- 单一职责原则
- Redux 入门了解
- Leetcode 134 Gas Station
- Redis之Set 集合类型
- python网络编程
- ue4 AddLocalOffset 不起作用
- 教父大片经典语录
- AsyncTask(二)AsyncTask源码分析(基于android-24)
- 极限初学者常遇到的几个坑(一)
- 开发网站合集
- Kettle 6.x 源码开发环境搭建