976 Largest Perimeter Triangle.py

#!/usr/bin/python3
"""
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
"""
from typing import List


class Solution:
    def largestPerimeter(self, A: List[int]) -> int:
        """
        sort and scanning from right
        """
        A.sort()
        for i in range(len(A) - 3, -1, -1):
            if A[i] + A[i+1] > A[i+2]:
                return sum(A[i:i+3])
        else:
            return 0