[leetcode]Gas Station

问题描述：

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.

代码：

int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {  //C++
if(gas.size()==0|| cost.size()==0||gas.size()!=cost.size())
return -1;

int size = gas.size();
vector<int> left(size);
for(int i=0; i<size; i++)
left[i]=gas[i]-cost[i];

int max=left[0],begin=0,temp=0,index=begin;
for(int i=0; i<size; i++ ){
temp += left[i];
if(temp > max){
max = temp;
index = begin;
}
if(temp < 0){
temp = 0;
begin = i+1;
}
}
if(temp >=0 && begin !=0){
for(int i=0; i<size; i++){
temp += left[i];
if(temp > max){
max =temp;
index = begin;
}
if(temp <0)
break;
}
}
temp = 0;
for(int i=0; i<size; i++ )
{
temp +=left[(i+index)%size];
if(temp <0)
return -1;
}
return index;
}