Find the Maximum Length of Valid Subsequence II - LeetCode Medium

3202. Find the Maximum Length of Valid Subsequence II

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You are given an integer array nums and a positive integer k.

A subsequence sub of nums with length x is called valid if it satisfies:

(sub[0] + sub[1]) % k == (sub[1] + sub[2]) % k == ... == (sub[x - 2] + sub[x - 1]) % k.

Return the length of the longest valid subsequence of nums.

Example 1:

Input: nums = [1,2,3,4,5], k = 2

Output: 5

Explanation:

The longest valid subsequence is [1, 2, 3, 4, 5].

Example 2:

Input: nums = [1,4,2,3,1,4], k = 3

Output: 4

Explanation:

The longest valid subsequence is [1, 4, 1, 4].

Constraints:

Hints

Hint 1

Fix the value of (subs[0] + subs[1]) % k from the k possible values. Let it be val.

Hint 2

Let dp[i] store the maximum length of a subsequence with its last element x such that x % k == i.

Hint 3

Answer for a subsequence ending at index y is dp[(k + val - (y % k)) % k] + 1.