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Kotlin-based LeetCode algorithm problem solutions, regularly updated

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134\. Gas Station

Medium

There are `n` gas stations along a circular route, where the amount of gas at the i^th station is `gas[i]`.

You have a car with an unlimited gas tank and it costs `cost[i]` of gas to travel from the i^th 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, otherwise return_ `-1`. If there exists a solution, it is **guaranteed** to be **unique**

**Example 1:**

**Input:** gas = [1,2,3,4,5], cost = [3,4,5,1,2]

**Output:** 3

**Explanation:** 

Start at station 3 (index 3) and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 

Travel to station 4. Your tank = 4 - 1 + 5 = 8 

Travel to station 0. Your tank = 8 - 2 + 1 = 7 

Travel to station 1. Your tank = 7 - 3 + 2 = 6 

Travel to station 2. Your tank = 6 - 4 + 3 = 5 

Travel to station 3. The cost is 5. Your gas is just enough to travel back to station 3. 

Therefore, return 3 as the starting index.

**Example 2:**

**Input:** gas = [2,3,4], cost = [3,4,3]

**Output:** -1

**Explanation:** You can't start at station 0 or 1, as there is not enough gas to travel to the next station. 

Let's start at station 2 and fill up with 4 unit of gas. Your tank = 0 + 4 = 4 

Travel to station 0. Your tank = 4 - 3 + 2 = 3 

Travel to station 1. Your tank = 3 - 3 + 3 = 3 

You cannot travel back to station 2, as it requires 4 unit of gas but you only have 3. 

Therefore, you can't travel around the circuit once no matter where you start.

**Constraints:**

*   `n == gas.length == cost.length`
*   1 <= n <= 10⁵
*   0 <= gas[i], cost[i] <= 10⁴