Leetcode NO.134 Gas Station

本题题目要求如下：

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.
这题算是比较简单的一道题



就用这张图片来说明吧。。我的算法是寻找最低点。。也就是4，只有从4出发，才有可能避免出现负数点。。。

当然我上面画的是连续图，如果是用离散的话，会有一点小的出入，但总体是这个意思。。

代码如下：

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
    	int concave_x = 0;
    	int concave_y = 0;
    	int remain = 0;
        int sz = gas.size();
        for(int i = 0; i < sz; ++i) {
        	remain = remain + gas[i] - cost[i];
        	concave_y = min(remain, concave_y);
        	if (remain == concave_y)
        		concave_x = i;
        }
       	if (remain < 0)
       		return -1;
       	else
        	return ((concave_x + 1) % sz);
    }
};