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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 <= 100001 <= A[i] <= 10^6
思路：结果一定是排序后连续的3个数，用反证法可以证明：如果不连续可以满足三角形约数，那么最大数后面连续的3个数也一定满足
class Solution:
def largestPerimeter(self, A):
"""
:type A: List[int]
:rtype: int
"""
A.sort(reverse=True)
for i in range(len(A)-2):
if A[i]-A[i+1]<A[i+2]:
return sum(A[i:i+3])
return 0