This issue is about [Longest Common Subsequence].

• Issue Title is in form LCS [C++].
• I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• This Algo/DS is worth adding to this repository.
• Assign this issue to me (I want to work on this).
  • I ensure that I am not already assigned to 2 or more issues.
• I will send my PR only after I'm assigned to this issue by any maintainer.
• I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.