Leetcode152: Gas Station

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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.

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