A sequence x1, x2, ..., xn is Fibonacci-like if:
- n >= 3
- xi + xi+1 == xi+2 for all i + 2 <= n
Given a strictly increasing array arr of positive integers forming a sequence, return the length of the longest Fibonacci-like subsequence of arr. If one does not exist, return 0.
A subsequence is derived from another sequence arr by deleting any number of elements (including none) from arr, 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: arr = [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: arr = [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].
Solution
class Solution:
def lenLongestFibSubseq(self, arr: List[int]) -> int:
s = set(arr)
res = 2
for i in range(len(arr)):
for j in range(i + 1, len(arr)):
a, b, l = arr[i], arr[j], 2
while a + b in s:
a, b, l = b, a + b, l + 1
res = max(res, l)
return res if res > 2 else 0