# 873. Length of Longest Fibonacci Subsequence LeetCode Solution Share:

Length of Longest Fibonacci Subsequence 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`.

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].```

Constraints:

• `3 <= arr.length <= 1000`
• `1 <= arr[i] < arr[i + 1] <= 109`

Time: O(n)
Space: O(n)

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