LeetCode:Gas Station

Gas Station

Total Accepted: 57248 Total
Submissions: 212077 Difficulty: Medium

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.

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Greedy

Explanation

If car starts at A and can not reach B. Any station between A and B can not reach B.
If the total number of gas is bigger than the total number of cost. There must be a solution.

class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        
        int sumGas = 0, sumCost = 0;
        int tank = 0;
        int start = 0;
        for(int i=0;i<gas.size();i++) {
            sumGas += gas[i];
            sumCost += cost[i];
            tank += gas[i] - cost[i];
            if(tank < 0) {
                start = i + 1;
                tank = 0;
            }
        }
        if(sumGas - sumCost < 0) return -1;
        else return start;
    }
};