[LeetCode] 873. Length of Longest Fibonacci Subsequence

ProblemA sequence X_1, X_2, …, X_n is fibonacci-like if:n >= 3X_i + X_{i+1} = X_{i+2} for all i + 2 <= nGiven 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: 5Explanation:The longest subsequence that is fibonacci-like: [1,2,3,5,8].Example 2:Input: [1,3,7,11,12,14,18]Output: 3Explanation:The longest subsequence that is fibonacci-like:[1,11,12], [3,11,14] or [7,11,18].Note:3 <= A.length <= 10001 <= A[0] < A[1] < … < A[A.length - 1] <= 10^9(The time limit has been reduced by 50% for submissions in Java, C, and C++.)Solutionclass Solution { public int lenLongestFibSubseq(int[] A) { Set<Integer> set = new HashSet<>(); for (int a: A) set.add(a); int max = 2; for (int i = 0; i < A.length-1; i++) { for (int j = i+1; j < A.length; j++) { int a1 = A[i], a2 = A[j]; int curMax = 2; while (set.contains(a1+a2)) { curMax++; int temp = a1; a1 = a2; a2 = temp+a2; } max = Math.max(max, curMax); } } return max == 2 ? 0 : max; }}