Gas Station

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.

Given two integer arrays gas and cost, return the starting gas station's index if you can travel around the circuit once in the clockwise direction. If there is no such starting station, return -1.

If a solution exists, it is guaranteed to be unique.

Examples

Example 1:

Input: gas = [1, 2, 3, 4, 5], cost = [3, 4, 5, 1, 2]
Output: 3
Explanation:
  Start at station 3 (gas = 4).
  Tank = 0 + 4 = 4
  Travel to station 4: Tank = 4 - 1 + 5 = 8
  Travel to station 0: Tank = 8 - 2 + 1 = 7
  Travel to station 1: Tank = 7 - 3 + 2 = 6
  Travel to station 2: Tank = 6 - 4 + 3 = 5
  Travel to station 3: Tank = 5 - 5 = 0
  You arrive back at station 3 with 0 gas left. Circuit complete.

Example 2:

Input: gas = [2, 3, 4], cost = [3, 4, 3]
Output: -1
Explanation: No matter which station you start at, you cannot
  complete the circuit. Total gas = 9, total cost = 10.

Example 3:

Input: gas = [5], cost = [4]
Output: 0
Explanation: Only one station. Start there, travel back to it.
  Tank = 5 - 4 = 1 >= 0. Circuit complete.

Constraints

• 1 <= n <= 10^5
• 0 <= gas[i], cost[i] <= 10^4
• n == gas.length == cost.length

Expected Complexity

• Time: O(n)
• Space: O(1)