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.

这题理解题意之后很简单，即要保证gas - cost 的和一直是正的就可以了。 但是要注意这是一个circular。

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(gas.length == 0) return -1;
        for(int i = 0; i < gas.length; i ++){
            gas[i] = gas[i] - cost[i];
        }
        for(int i = 0; i < gas.length; i ++){
            int sum = 0;
            boolean sig = true;
            for(int j = i; j < gas.length; j ++){
                sum += gas[j];
                if(sum < 0){
                    sig = false;
                    break;
                }
            }
            for(int j = 0; j < i; j ++){
                sum += gas[j];
                if(sum < 0){
                    sig = false;
                    break;
                }
            }
            if(sig == true)return i;
        }
        return -1;
    }
}