976. Largest Perimeter Triangle-三角形的最大周长

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:

• 3 <= A.length <= 10000
• 1 <= A[i] <= 10^6
  Solution in python:

  class Solution:
  def largestPerimeter(self, A: List[int]) -> int:
      A.sort()
      for i in range(len(A)-1, 1, -1):
          if A[i-1] + A[i-2] > A[i]:
              return A[i]+A[i-1]+A[i-2]
      else:
          return 0