Gas Station
There are n gas stations along a circular route, where the amount of gas at the ith station is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from the ith station to its next (i+1)th station. 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 in a clockwise direction, otherwise return -1.
Constraints:
- n == gas.length == cost.length
- 1 <= n <= 10^4
- 0 <= gas[i], cost[i] <= 10^4
- gas[i] and cost[i] are non-negative integers
Examples:
Input: [1,2,3,4,5],[3,4,5,1,2]
Output: 3
Explanation: Start at station 3 (index 3) and fill up with 4 units of gas. Travel to station 4 and fill up with 5 units of gas. Travel to station 0 and fill up with 1 unit of gas. Travel to station 1 and fill up with 2 units of gas. Travel to station 2 and fill up with 3 units of gas. Travel to station 3 and fill up with 4 units of gas, completing the circuit.
Solutions
Greedy Algorithm
The solution uses a greedy algorithm to find the starting gas station. It iterates through the gas stations, keeping track of the total amount of gas and the amount of gas in the tank. If the tank becomes empty, it resets the starting station and the tank. If the total amount of gas is non-negative, it returns the starting station; otherwise, it returns -1.
public int canCompleteCircuit(int[] gas, int[] cost) {
int total = 0, tank = 0, start = 0;
for (int i = 0;
i < gas.length;
i++) {
int diff = gas[i] - cost[i];
total += diff;
tank += diff;
if (tank < 0) {
start = i + 1;
tank = 0;
}
}
return total >= 0 ? start : -1;
}Follow-up:
What if the gas stations are not along a circular route?
