1018 Largest Perimeter Triangle

Largest Perimeter Triangle

Given an integer array nums, return the largest perimeter of a triangle with a non-zero area, formed from three of these lengths. If it is impossible to form any triangle of a non-zero area, return 0.

 

Example 1:

**Input:** nums = [2,1,2]
**Output:** 5
**Explanation:** You can form a triangle with three side lengths: 1, 2, and 2.

Example 2:

**Input:** nums = [1,2,1,10]
**Output:** 0
**Explanation:** 
You cannot use the side lengths 1, 1, and 2 to form a triangle.
You cannot use the side lengths 1, 1, and 10 to form a triangle.
You cannot use the side lengths 1, 2, and 10 to form a triangle.
As we cannot use any three side lengths to form a triangle of non-zero area, we return 0.

 

Constraints:

3 <= nums.length <= 104
1 <= nums[i] <= 106

class Solution:
    def largestPerimeter(self, nums: List[int]) -> int:
        nums.sort(key= lambda x : -x)
        i = 0
        while(i + 2 < len(nums) and nums[i+2] + nums[i+1] <= nums[i]):
            i += 1
        if i + 2 == len(nums):
            return 0
        return nums[i + 1] + nums[i] + nums[i+2]