Implement longest-arithmetic-subsequence-of-given-difference

name: longest-arithmetic-subsequence-of-given-difference
url: https://leetcode.com/problems/longest-arithmetic-subsequence-of-given-difference
difficulty: 2

time: 60000 ms
time-rank: 0.0 %
time-complexity: O(N^2)

space: 100.0 MB
space-rank: 25.0 %
space-complexity: O(N)

Fixes #316

Signed-off-by: Christopher Friedt <[email protected]>

Author: cfriedt