Gas station Solution

Problem

There was N gas stations along a circular route, where the amount of gas at Station I was gas[i] .

You had a car with an unlimited gas tank and it costs of gas to travel from station cost[i] I to its next station (i+ 1). You begin the journey with a 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.

Solution

Key to the solution is a conclusion:

If sum of gas >= sum of costs, then there must exists one or more solution.

If sum of Gas < sum of costs, then there is no solution.

So we can use the method of exclusion here.

We need also note here is if a can not reach C in a the sequence of a-->b-->c and then B can does not make it either.

1  Public classSolution {2      Public intCancompletecircuit (int[] Gas,int[] cost) {3         if(Gas = =NULL|| Cost = =NULL)4             return-1;5         if(Gas.length! =cost.length)6             return-1;7         intStart = 0;8         intsumremaining = 0;9         inttotalremaining = 0;Ten          for(inti = 0; i < gas.length; i++) { One             intTMP = Gas[i]-Cost[i]; A             if(sumremaining >= 0) { -Sumremaining + =tmp; -}Else { theStart =i; -Sumremaining =tmp; -             } -Totalremaining + =tmp; +         } -         if(Totalremaining < 0) +             return-1; A         returnstart; at     } -}

Gas station Solution