134. Gas Station

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.

解法一：我的解法

class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        int n = gas.size();
        int left = 0, start = 0, end = 0;
        for(int i = 0; i < 2 * n - 1; i++ ){
            left += (gas[i % n] - cost[i % n]);
            if(left < 0){
                left = 0;
                start = i + 1;
            }
            else
            end = i + 1;
            if(end - start == n)
            
            return start;
        }
        return -1;
    }
};

解法二：其他解法

public int canCompleteCircuit(int[] gas, int[] cost) {
    int sumGas = 0;
    int sumCost = 0;
    int start = 0;
    int tank = 0;
    for (int i = 0; i < gas.length; i++) {
        sumGas += gas[i];
        sumCost += cost[i];
        tank += gas[i] - cost[i];
        if (tank < 0) {
            start = i + 1;
            tank = 0;
        }
    }
    if (sumGas < sumCost) {
        return -1;
    } else {
        return start;
    }
}