# Longest Arithmetic Subsequence with Difference Constraint

Given a list of integers `nums`

and an integer `diff`

, return the length of the longest arithmetic subsequence where the difference between each consecutive numbers in the subsequence is `diff`

.

**Constraints**

`0 ≤ n ≤ 100,000`

where`n`

is the length of`nums`

https://binarysearch.com/problems/Longest-Arithmetic-Subsequence-with-Difference-Constraint

## Examples

### Example 1

**Input**

- nums =
`[-2, 0, 3, 6, 1, 9]`

- diff =
`3`

**Output**

- answer =
`4`

**Explanation**

We can pick the subsequence `[0, 3, 6, 9]`

.

### Example 2

**Input**

- nums =
`[9, 8, 7, 5, 3]`

- diff =
`-2`

**Output**

- answer =
`4`

**Explanation**

We can pick the subsequence `[9, 7, 5, 3]`

.

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