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.

超时代码O(n²)：

class Solution{
  public:
      int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
          if(gas.empty()||cost.empty()) return -1;
          int myToalGas=0;
          int remain=0;
          for (int i=0;i<gas.size();++i)
          {
              int j=0;
              for (j;j<gas.size();++j)
              {
                  myToalGas=remain+gas[j];
                  remain=myToalGas-cost[j];
                  if(remain>=0) continue;
                  else break;
              }
              if(j==gas.size()) return i;
          }
          return -1;
      }
  };