[LeetCode 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.
 *
 */

public class GasStation {

	
//	16 / 16 test cases passed.
//	Status: Accepted
//	Runtime: 247 ms
//	Submitted: 0 minutes ago
	
	//時間復雜度O(n) 空間復雜度O(1)
    public int canCompleteCircuit(int[] gas, int[] cost) {
        
    	int remaining = 0;				//從開始點到當前點剩余的油量
    	int begin = -1;					//開始點下標
    	int total = 0;					//	判斷是否有解			
    	for (int i = 0; i < cost.length; i++) {
    		remaining += gas[i] - cost[i];
    		total += gas[i] - cost[i];
			if(remaining < 0) {
				remaining = 0;
				begin = i;
			}			
		}  
    	return (total < 0) ? -1 : begin + 1;
    }    
	public static void main(String[] args) {
		
	}

}