【LeetCode】Gas Station

参考链接

http://blog.csdn.net/jellyyin/article/details/12245429

http://blog.csdn.net/doc_sgl/article/details/12980297

题目描述

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.

题目分析

1. 每一站的代价为gas-cost, 也就是求从哪一站开始累加代价和总是大于0。

2. 如果所有站的代价和大于0，则所求的路线必定存在。

如果总代价〉=0,从序号0开始求代价和，如果代价和小于0，则不是从本站或者本站之前的某一个代价大于0的站开始，必从下一站即之后的站开始，而且这样的站必定存在。

总结

代码示例

class Solution {
public:
int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
// Note: The Solution object is instantiated only once.
int total = 0;
int currentgas = 0;
int startpoint = -1;
int sz = gas.size();
for(int i = 0; i < sz; i++)
{
currentgas += gas[i] - cost[i];
total += gas[i] - cost[i];
if(currentgas < 0)
{
startpoint = i;
currentgas = 0;
}
}
return total >= 0 ? startpoint+1 : -1;
}
};

推荐学习C++的资料

C++标准函数库
http://download.csdn.net/detail/chinasnowwolf/7108919

在线C++API查询
http://www.cplusplus.com/

vector使用方法

http://www.cplusplus.com/reference/vector/vector/