A sequence X_1, X_2, ..., X_n is fibonacci-like if:
n >= 3
X_i + X_{i+1} = X_{i+2} for all i + 2 <= n
Given a strictly increasing array A of positive integers forming a sequence, find the length of the longest fibonacci-like subsequence of A.  If one does not exist, return 0.
(Recall that a subsequence is derived from another sequence A by deleting any number of elements (including none) from A, without changing the order of the remaining elements.  For example, [3, 5, 8] is a subsequence of [3, 4, 5, 6, 7, 8].)
Example 1:
Input: [1,2,3,4,5,6,7,8]
Output: 5
Explanation:
The longest subsequence that is fibonacci-like: [1,2,3,5,8].
Example 2:
Input: [1,3,7,11,12,14,18]
Output: 3
Explanation:
The longest subsequence that is fibonacci-like:
[1,11,12], [3,11,14] or [7,11,18].
Note:
3 <= A.length <= 1000
1 <= A[0] < A[1] < ... < A[A.length - 1] <= 10^9
(The time limit has been reduced by 50% for submissions in Java, C, and C++.)
class Solution:
    def lenLongestFibSubseq(self, A: List[int]) -> int:
        set_a = set(A)
        res = 0
        for i in range(len(A)):
            for j in range(i+1, len(A)):
                x, y = A[i], A[j]
                leng = 2
                while x+y in set_a:
                    x, y = y, x+y
                    leng += 1
                res = max(res, leng)
        return res if res >=3 else 0
class Solution:
    def lenLongestFibSubseq(self, A: List[int]) -> int:
        set_a = set(A)
        res = 0
        for i in range(len(A)):
            for j in range(i+1, len(A)):
                x, y = A[i], A[j]
                leng = 2
                while x+y in set_a:
                    x, y = y, x+y
                    leng += 1
                res = max(res, leng)
        return res if res >=3 else 0