976. Largest Perimeter Triangle

Given an array `A` of positive lengths, return the largest perimeter of a triangle with non-zero area, formed from 3 of these lengths.

If it is impossible to form any triangle of non-zero area, return `0`.

Example 1:

```Input: [2,1,2]
Output: 5
```

Example 2:

```Input: [1,2,1]
Output: 0
```

Example 3:

```Input: [3,2,3,4]
Output: 10
```

Example 4:

```Input: [3,6,2,3]
Output: 8
```

Note:

1. `3 <= A.length <= 10000`
2. `1 <= A[i] <= 10^6`

976. Largest Perimeter Triangle
``````struct Solution;

impl Solution {
fn largest_perimeter(mut a: Vec<i32>) -> i32 {
let n = a.len();
a.sort_unstable();
for i in (0..=n - 3).rev() {
if a[i] + a[i + 1] > a[i + 2] {
return a[i] + a[i + 1] + a[i + 2];
}
}
0
}
}

#[test]
fn test() {
let a = vec![2, 1, 2];
assert_eq!(Solution::largest_perimeter(a), 5);
let a = vec![1, 2, 1];
assert_eq!(Solution::largest_perimeter(a), 0);
let a = vec![3, 2, 3, 4];
assert_eq!(Solution::largest_perimeter(a), 10);
let a = vec![3, 6, 2, 3];
assert_eq!(Solution::largest_perimeter(a), 8);
}
``````