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g0801_0900.s0873_length_of_longest_fibonacci_subsequence.readme.md Maven / Gradle / Ivy

873\. Length of Longest Fibonacci Subsequence

Medium

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].

**Constraints:**

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