Gas Station leetcode java

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.

Note:
The solution is guaranteed to be unique.

题解：

网上搜到的解法。

据说是Bloomberg的面试题。

用两个变量存+= gas[i] - cost[i]。一个帮助判断当前这个点作为gas station的起点合不合适，一个帮助判断总的需求是不是大于供给。如果总的需求大于供给那么肯定是无解的，如果需求小于等于供给，就可以返回刚才找到的起始点。

代码如下：

 1     public int canCompleteCircuit(int[] gas, int[] cost) {
 2         if (gas==null|| cost==null||gas.length==0||cost.length==0||gas.length!=cost.length)
 3          return -1;
 4          
 5         int sum = 0;  
 6         int total = 0;  
 7         int index = 0;  
 8         for(int i = 0; i < gas.length; i++){  
 9             sum += gas[i]-cost[i];  
             total += gas[i]-cost[i];  
             if(sum < 0){  
                 index=i+1; 
                 sum = 0;   
             } 
         }  
         if(total<0)
             return -1;  
         else
             return index;  
     }

Reference：http://blog.csdn.net/lbyxiafei/article/details/12183461