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.

Idea:

@daxianji007 said in Share some of my ideas.:

I have thought for a long time and got two ideas:

• If car starts at A and can not reach B. Any station between A and B can not reach B.(B is the first station that A can not reach.)
• If the total number of gas is bigger than the total number of cost. There must be a solution.
• (Should I prove them?)

Here is my solution based on those ideas:

    class Solution {
    public:
        int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
            int start(0),total(0),tank(0);
            //if car fails at 'start', record the next station
            for(int i=0;i<gas.size();i++) if((tank=tank+gas[i]-cost[i])<0) {start=i+1;total+=tank;tank=0;}
            return (total+tank<0)? -1:start;
        }
    };

Solution:

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start = 0, total = 0, tank = 0;
        for(int i = 0; i < gas.length; i++){
            tank = tank+gas[i];
            if(tank - cost[i] < 0){ 
                start = i + 1;
                total = total +gas[i]  -cost[i];
                tank = 0;
                continue;
            }
            tank = tank-cost[i];
            total = total+gas[i]-cost[i];
        }
        if(total >= 0) return start;
        return -1;
    }
}