941. Valid Mountain Array

Given an array of integers `arr`, return `true` if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:

• `arr.length >= 3`
• There exists some `i` with `0 < i < arr.length - 1` such that:
• `arr[0] < arr[1] < ... < arr[i - 1] < arr[i] `
• `arr[i] > arr[i + 1] > ... > arr[arr.length - 1]`

Example 1:

```Input: arr = [2,1]
Output: false
```

Example 2:

```Input: arr = [3,5,5]
Output: false
```

Example 3:

```Input: arr = [0,3,2,1]
Output: true
```

Constraints:

• `1 <= arr.length <= 104`
• `0 <= arr[i] <= 104`

941. Valid Mountain Array
``````struct Solution;

impl Solution {
fn valid_mountain_array(a: Vec<i32>) -> bool {
let n = a.len();
if n < 3 {
return false;
}
let mut i = 0;
while i + 1 < n && a[i] < a[i + 1] {
i += 1;
}
if i == 0 || i == n - 1 {
return false;
}
while i + 1 < n && a[i] > a[i + 1] {
i += 1;
}
i == n - 1
}
}

#[test]
fn test() {
let a = vec![2, 1];
assert_eq!(Solution::valid_mountain_array(a), false);
let a = vec![3, 5, 5];
assert_eq!(Solution::valid_mountain_array(a), false);
let a = vec![0, 3, 2, 1];
assert_eq!(Solution::valid_mountain_array(a), true);
}
``````