873. 最长的斐波那契子序列的长度

class Solution:
    def lenLongestFibSubseq(self, A: List[int]) -> int:
        
        s = set(A)
        n = len(A)
        result = 0
        
        for i in range(n-1):
            for j in range(i+1, n):
                a, b = A[i], A[j]
                count = 2
                while a+b in s:
                    a, b = b, a+b
                    count += 1
                    # A= [1,2,3,4,5,6,7,8]
                    # [1,2,3,5,8] 
                    # [1,3,4,7] 
                    # [1,4,5]
                    # ...
                    # 取其中最大的序列长度
                    result = max(result, count)
        return result if result > 2 else 0