# 14.07.2023 [1218. Longest Arithmetic Subsequence of Given Difference]

Longest arithmetic `difference` subsequence

14.07.2023

1218. Longest Arithmetic Subsequence of Given Difference medium
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Problem TLDR

Longest arithmetic difference subsequence

Intuition

Store the next value and the length for it.

Approach

We can use a HashMap

Complexity

• Time complexity:
  O(n)

• Space complexity:
  O(n)

Code

fun longestSubsequence(arr: IntArray, difference: Int): Int = 
with(mutableMapOf<Int, Int>()) {
    arr.asSequence().map { x ->
        (1 + (this[x] ?: 0)).also { this[x + difference] = it } 
    }.max()!!
}