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Leetcode 134 Gas Station.

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.


There are two general ideas here:
1.If the total cost is more than the total gas available, then, there should not have any possibility to reach the end.
2.If you can reach the next station, you should only consider how much gas you have.



public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start=0;
        int tank=0;
        int totalgas=0;
        int totalcost=0;
        for(int i=0;i < gas.length;i++){
            totalgas+=gas[i];
            totalcost+=cost[i];
        }


        for(int i=0;i < gas.length;i++){
            tank=tank+gas[i]-cost[i];
            if(tank<0){
                start=i+1;
                tank=0;
            }
        }


        if(totalcost > totalgas){
            return -1;
        }else{
            return start;
        }
    }
}
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