Comments on: Extract Longest Non-Decreasing Sequence From Any Sequence

By: olhovsky

olhovsky — Thu, 31 Mar 2011 17:33:41 +0000

@Thanh: It’s trivial to modify the algorithm I gave to produce the longest non-decreasing subsequence, instead of the longest increasing subsequence. In fact, I think it’s just a matter of changing/adding a few characters. What application do you have in mind by the way? I had no application in mind when solving this problem — a professor of mine claimed to have an O(n^2) solution, so I produced an O(n log n) algorithm in response.

By: Thanh

Thanh — Thu, 31 Mar 2011 11:29:02 +0000

This problem with your algorithm is not applicable.
Write an algorithm which reads a sequence of real numbers and determines the length of the longest non-decreasing subse-
quence. For instance, in the sequence
7,8,7,8,9,2,1,8,7,9,9,10,10,9,
the longest non-decreasing subsequence is 7,9,9,10,10, of length 5.

By: Problem Solving: Growing Sequences « My Trip Through CSC165

Problem Solving: Growing Sequences « My Trip Through CSC165 — Wed, 08 Dec 2010 17:00:55 +0000

[...] Somebody wrote a program for finding the longest non-decreasinging subsequence in a list. Assuming that it’s correct, I was able to check my solution with it, and I found that I got the same result. There are other ways for deriving the solution, also. I could have started with the first number. But this would be a lot more tedious, as I would have to check many more subsequences since I wouldn’t have the knowledge of the lengths of subsequence sub-sub-sequences. We only care about getting the longest, and starting with the first, I would end up getting a list like such: [...]

By: brian

brian — Thu, 08 Jul 2010 15:20:29 +0000

Nice to know it’s here if I ever need it. I like the format of the listing too (fixed pitch, alternating shading).

By: olhovsky

olhovsky — Thu, 13 May 2010 23:29:52 +0000

Hey someone found a use for this?! Well, that’s more than I expected when posting it

By: newur

newur — Thu, 06 May 2010 05:25:57 +0000

Hey,

that was (nearly) excact what i was looking for. Had to write this for univerisity in Java. In the end my resulting code looks MUCH different and is not as fast as yours, but its still okay. Without your example I would have never find a solution (and it took only 3 Hours of try-and-error to understand, how it works ^^)

Thanks for sharing, man.

By: olhovsky

olhovsky — Tue, 20 Apr 2010 06:08:12 +0000

Can you be a little bit more specific?
E.g., tell me a sequence that this algorithm doesn’t work on.

I have verified this against a few million random strings which were solved using a more brute force approach, so I’d be surprised if there is an error.

By: Mac

Mac — Fri, 09 Apr 2010 00:19:01 +0000

Yo, this shit doesn’t fucking work