Leetcode 1087 Solution

This article provides solution to leetcode question 1087 (longest-arithmetic-subsequence)
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https://leetcode.com/problems/longest-arithmetic-subsequence

Solution

class Solution:
    def longestArithSeqLength(self, A: List[int]) -> int:
        dp = collections.defaultdict(int)
        ans = 0
        for i in range(len(A)):
            for j in range(i):
                d = A[i] - A[j]
                dp[(d, i)] = dp[(d, j)] + 1
                ans = max(dp[(d, i)], ans)
        return ans + 1