data structures - Binary search over 2d array to find a local maximum? What's wrong with this algorithm? -


this classic finding local maximum (just one) in matrix.

my algorithm is:

  • choose number in center of matrix.
  • check if number peak. if yes, return.

  • if not, check numbers left , right. if 1 of them greater our current number, choose half of matrix. if both greater, can choose either half.

  • repeat numbers top , bottom. leave 1 quadrant of matrix continue checking.

since binary search n x n matrix has n^2 elements, should take o(log(n^2)) = o(2*log(n)) = o(log(n))

i'm pretty sure not correct, mistake?

this algorithm isn't guaranteed find local maximum. consider example case need follow winding path through matrix of ascending values peak. if path crosses , forth between quadrants algorithm not find it.

13  1  1  1  1 12  1  1  1  1 11  1  1  2  3 10  1  1  1  4  9  8  7  6  5

or, here's simpler example:

3  1  1  1  1 1  1  1  1  1 1  1  1  1  1 1  1  1  1  1 1  1  1  1  1

you start in middle, how find '3'? algorithm doesn't describe when faced horizontal plane.


Comments

Post a Comment

Popular posts from this blog

resizing Telegram inline keyboard -

telegram's inline keyboard great feature lots of different use cases. inline buttons added list of items this: inline_keyboard = [[inlinekeyboardbutton(text="button", callback_data="button"), inlinekeyboardbutton(text="reset",callback_data="reset")]] inline_keyboard_markup = inlinekeyboardmarkup(inline_keyboard) update.message.reply_text("hi", reply_markup=inline_keyboard_markup) the above code adds 2 buttons each half width of chat screen. i know the normal keyboard button there resize_keyboard parameter somehow can used. my question is there way resize inline buttons ? example make full width or quarter width. unfortunately, can't now. :( you can suggest @botsupport , might add feature next version.
Read more

command line - How can a Python program background itself? -

consider following python command-line program. doesn't work because incomplete, think illustrates problem: #!/usr/bin/python3 import multiprocessing pool = multiprocessing.pool() task in expensive_iterator_with_user_interaction(): pool.call_async(expensive_computation, (task,)) pool.close() print("dear user, may press ctrl-z , bg script.") pool.join() thus, problem scripts needs user input while it's launching expensive parallel processes. there moment when user interaction not needed anymore. then, ask user background process shell actions. however, can achieved program itself? (side note: core of problem entanglement of user input firing “expensive computations”. therefore, cannot separate both in 2 scripts, , letting 1 spawning other daemon.) the command screen may you. use screen -l create new session , run application. after inputting data, can press " ctrl-a " , press " d " on keyboard detach session. now
Read more

php - "cURL error 28: Resolving timed out" on Wordpress on Azure App Service on Linux -

Image
my wordpress installation on azure app service on linux using custom docker container has slow response times. pages take around 20-40 seconds load. i have troubleshooting plugin installed indicates problem "curl error 28: resolving timed out after n milliseconds" when making requests following urls https://api.wordpress.org/core/version-check/1.7/ http://api.wordpress.org/core/version-check/1.7/ https://api.wordpress.org/plugins/update-check/1.1/ http://api.wordpress.org/plugins/update-check/1.1/ https://api.wordpress.org/themes/update-check/1.1/ http://api.wordpress.org/themes/update-check/1.1/ curl works fine on scm-site command line. example works ok. curl -x post http://api.wordpress.org/core/version-check/1.7/ edit if ssh container , run php code, works fine. <?php $url = 'http://api.wordpress.org/core/version-check/1.7/'; $fields = array( 'version' => urlencode('4.8.1'), 'php' => urlencode(
Read more