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873. Length of Longest Fibonacci Subsequence

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Description

A sequence X_1, X_2, ..., X_n is fibonacci-like if:

<li><code>n &gt;= 3</code></li>

<li><code>X_i + X_{i+1} = X_{i+2}</code>&nbsp;for all&nbsp;<code>i + 2 &lt;= n</code></li>

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:

<li><code>3 &lt;= A.length &lt;= 1000</code></li>

<li><code>1 &lt;= A[0] &lt; A[1] &lt; ... &lt; A[A.length - 1] &lt;= 10^9</code></li>

<li><em>(The time limit has been reduced by 50% for submissions in Java, C, and C++.)</em></li>

Solutions

Python3

Java

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