[letcode 134] Gas Station

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本文介绍了一个算法问题，即如何在一个包含多个加油站的环形路线上找到一个起点，使得一辆初始油箱为空的汽车能够绕环形路线一周。该问题通过遍历每个加油站并计算累积的油量变化来解决，如果总油量变化为正，则返回可行的起始加油站的索引。

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.

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
        int sum = 0;
        int cur = 0;
        int start = 0;
        const int n = gas.size();
        for (int i = 0; i < n ; i++) {
            sum += gas[i] - cost[i];
            cur += gas[i] - cost[i];
            if (cur < 0) {
                cur = 0;
                start = i+1;
            }
        }
        return sum<0?-1:start;
    }
};