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

Rust Solution

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);
}

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