Written by Ron on 010111 April 000112011. Posted in Blog

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

Example 2:
Input: nums = [1,2,1]
Output: 0
 
Constraints:
3 <= nums.length <= 104
1 <= nums[i] <= 106

from typing import List

class Solution:
    def largestPerimeter(self, nums: List[int]) -> int:
        _len = len(nums)
        nums.sort()
        
        for i in range(_len-1, 1, -1): #range(start, stop, step)
            if nums[i] < nums[i-1] + nums[i-2]:
                return nums[i] + nums[i-1] + nums[i-2]
        return 0
        
s = Solution()
        
print(s.largestPerimeter([3,2,2,1,1,3,1]))#8
print(s.largestPerimeter([3,2,3,4]))#10
print(s.largestPerimeter([2,1,2]))#5
print(s.largestPerimeter([1,2,1]))#0