Leetcode 873. Length of Longest Fibonacci Subsequence

Given a strictly increasing array of positive integers, find the length of the longest subsequence (not necessarily contiguous) that is Fibonacci-like — i.e., every element from the third equals the sum of the two preceding ones — or return 0 if none exists. Constraints: 3 ≤ n ≤ 1000 and values ≤ 1e9, so solutions typically exploit pairwise relationships (DP/hash) to build lengths efficiently.