LeetCode 134. Gas Station

Problem :https://leetcode.com/problems/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.

 

Code C++:

class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        vector<int> left;
        for (int i = 0; i < gas.size(); i++) {
            left.push_back(gas[i] - cost[i]);
        }
        
        int total = 0, sub = INT_MAX,start = 0;
        for (int i = 0; i < left.size(); i++) {
            total += left[i];
            if (total < sub) {
                sub = total;
                start = i + 1;
            }
        }
        return (total < 0) ? -1 : start%left.size();
    }
};