There are `n`

gas stations along a circular route, where the amount of gas at the `i`

station is ^{th}`gas[i]`

.

You have a car with an unlimited gas tank and it costs `cost[i]`

of gas to travel from the `i`

station to its next ^{th}`(i + 1)`

station. You begin the journey with an empty tank at one of the gas stations.^{th}

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:3Explanation: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:-1Explanation: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:**

`gas.length == n`

`cost.length == n`

`1 <= n <= 10`

^{4}`0 <= gas[i], cost[i] <= 10`

^{4}

```
struct Solution;
impl Solution {
fn can_complete_circuit(gas: Vec<i32>, cost: Vec<i32>) -> i32 {
let n = gas.len();
let mut total = 0;
let mut cur = 0;
let mut idx = 0;
for i in 0..n {
total += gas[i] - cost[i];
cur += gas[i] - cost[i];
if cur < 0 {
idx = i + 1;
cur = 0;
}
}
if total >= 0 {
idx as i32
} else {
-1
}
}
}
#[test]
fn test() {
let gas = vec![1, 2, 3, 4, 5];
let cost = vec![3, 4, 5, 1, 2];
let res = 3;
assert_eq!(Solution::can_complete_circuit(gas, cost), res);
}
```