#1027
Longest Arithmetic Subsequence
medium · verified · 49.9% accepted · 4,905 likes · top 37%
array · hash table · binary search · dynamic programming
Description
Given an array nums of integers, return the length of the longest arithmetic subsequence in nums.
Note that:
- A subsequence is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.
- A sequence seq is arithmetic if seq[i + 1] - seq[i] are all the same value (for 0 <= i < seq.length - 1).
Example 1:
Input: nums = [3,6,9,12]
Output: 4
Explanation: The whole array is an arithmetic sequence with steps of length = 3.
Example 2:
Input: nums = [9,4,7,2,10]
Output: 3
Explanation: The longest arithmetic subsequence is [4,7,10].
Example 3:
Input: nums = [20,1,15,3,10,5,8]
Output: 4
Explanation: The longest arithmetic subsequence is [20,15,10,5].
Solution