[LeetCode 题解]：Gas Station

前言

【LeetCode 题解】系列传送门：  http://www.cnblogs.com/double-win/category/573499.html

1.题目描述

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.

2. 思路

题解： 与经典的最大字段和问题类似，采用贪心策略。

3. 解法

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
        int station = gas.size();
        int i,sum=0,start=0,total=0;
        
        for(i=0;i<station;i++)
            gas[i]-=cost[i];
        
        for(i=0;i<station;i++) total+=gas[i];
        if(total<0) return -1;
     
       // 与求最大子段和类似，使用贪心策略   
        for(i=0;i<station;i++)
        {
              sum+= gas[i];
              if(sum<0)
              {
                  start=i+1;  // 如果当前和为负数，选择下一个元素作为起点
                  sum=0;
              }
        }
        return start;      
    }
};

4. 相关题目

Maximum Subarray : http://www.cnblogs.com/double-win/p/3746672.html

作者：Double_Win 出处:   http://www.cnblogs.com/double-win/p/3746637.html 声明： 由于本人水平有限，文章在表述和代码方面如有不妥之处，欢迎批评指正~