[Medium]Gas Station

问题：
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.

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解法：

源码：

class Solution {public:    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {        int n = gas.size();        if (!n) return -1;        int a[n], b[n];        memset(b, 0, sizeof(b));        for (int i = 0; i < n; ++i) a[i] = gas[i] - cost[i];        b[0] = a[0];        for (int i = 1; i < n; ++i) b[i] = b[i-1] + a[i];        if (b[n-1] < 0) return -1;        int maxx = a[0] - b[0], maxi = 0;        for (int i = 1; i < n; ++i) {            if (a[i]  - b[i] > maxx) {                maxx = a[i] - b[i];                maxi = i;            }        }        return maxi;    }};