Leetcode - Length of Longest Fibonacci Subsequence

https://leetcode.com/problems/length-of-longest-fibonacci-subsequence/

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

• n >= 3
• X_i + X_{i+1} = X_{i+2} for all i + 2 <= n

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].

func lenLongestFibSubseq(A []int) int {
    if len(A) == 0 {
        return 0
    }
    n := len(A)
    dp := make([][]int, n)
    max := 0
    for i := 0; i < len(dp); i++ {
        dp[i] = make([]int, n)
    }
    dp[0][0] = 1
    for i := 2; i < n; i++ {
        l := 0
        r := i - 1
        for l < r {
            sum := A[l] + A[r]
            if sum == A[i] {
                dp[r][i] = dp[l][r] + 1
                if dp[r][i] > max {
                    max = dp[r][i]
                }
                l++
                r--
                continue
            }
            if sum > A[i] {
                r--
            } else {
                l++
            }
        }
    }
    if max == 0 {
        return max
    }
    return max + 2
}

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