Algorithms

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Re: finding all recurring elements in an array Rocky#17-Jul-07 7:13 Rocky# 17-Jul-07 7:13  yea i guess there's no other option but to use brute force Re: finding all recurring elements in an array Luc Pattyn17-Jul-07 7:28 Luc Pattyn 17-Jul-07 7:28  well, what did you expect ? Here are two approaches without any visible sorting: 1. just enter the numbers one by one in a hashtable; use the numbers as the key, and their multiplicity as the value. So to add a[i], check for presence of key a[i]; if not, add the pair (a[i], 1), else replace (a[i], value) by (a[i], value+1). When done, enumerate the keys with value>=2 2. Since you are not interested in actual multiplicity values, you could try two simple lists: one for "seen just once", the other for "seen more than once". Now for each a[i] first test the "more than once", if not present, the "just once", and move/add the item appropriately. Dont be surprised if this takes longer, for new numbers you are searching two lists (albeit they both are smaller). For both of the above methods, here is a big optimization: just do it for all numbers but the last one. If these all appear more than once, there is no need to read the last number at all. Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: finding all recurring elements in an array PICguy22-Jul-07 12:10 PICguy 22-Jul-07 12:10  If you want the elements themselves simply sort your list. If you also need the original index values you will have to sort element numbers along with the elements. After sorting the problem becomes trivial. Interesting math magic? Paul Conrad15-Jul-07 12:35 Paul Conrad 15-Jul-07 12:35  Math Magic on Yahoo[^] Anybody see the "trick"? "The clue train passed his station without stopping." - John Simmons / outlaw programmer Re: Interesting math magic? cp987616-Jul-07 12:49 cp9876 16-Jul-07 12:49  Careful - some educator may adopt it into 'New Math'. For those who haven't heard the Tom Lehrer song New Math[^] Peter "Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time." Re: Interesting math magic? MarkB77716-Jul-07 23:14 MarkB777 16-Jul-07 23:14  haha, I think i'd rather just stick with my calculator . Mark. Re: Interesting math magic? Luc Pattyn16-Jul-07 23:25 Luc Pattyn 16-Jul-07 23:25  And how do you think your calculator performs its magic ? Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: Interesting math magic? MarkB77716-Jul-07 23:33 MarkB777 16-Jul-07 23:33  hmmm... Is it a small black box which houses a microscopic chinese guy inside who is able to almost instantanously solve any mathematical equation you throw at him? Re: Interesting math magic? Paul Conrad17-Jul-07 7:33 Paul Conrad 17-Jul-07 7:33  "The clue train passed his station without stopping." - John Simmons / outlaw programmer Re: Interesting math magic? PIEBALDconsult17-Jul-07 7:37 PIEBALDconsult 17-Jul-07 7:37  Nah, Polish. Re: Interesting math magic? stevepqr7-Aug-07 6:07 stevepqr 7-Aug-07 6:07  is that a regular Polish guy or a reverse Polish? Apathy Rules - I suppose... Re: Interesting math magic? PIEBALDconsult17-Jul-07 7:36 PIEBALDconsult 17-Jul-07 7:36  Trick? What trick? It's the same as usual, but maybe helps some people keep the columns aligned properly. Re: Interesting math magic? Paul Conrad17-Jul-07 7:42 Paul Conrad 17-Jul-07 7:42  PIEBALDconsult wrote: It's the same as usual Yes it is. Just a different twist to it. "The clue train passed his station without stopping." - John Simmons / outlaw programmer Re: Interesting math magic? Bassam Abdul-Baki19-Jul-07 5:10 Bassam Abdul-Baki 19-Jul-07 5:10  The previous one was done with sticks, this one just makes it easier for the layman to understand. "This perpetual motion machine she made is a joke. It just keeps going faster and faster. Lisa, get in here! In this house, we obey the laws of thermodynamics!" - Homer Simpson Web - Blog - RSS - Math - LinkedIn - BM Re: Interesting math magic? _Damian S_17-Jul-07 16:56 _Damian S_ 17-Jul-07 16:56  That looked like a whole lot of hard work to me... just do it the normal way and be done with it!! ------------------------------------------- Don't walk in front of me, I may not follow; Don't walk behind me, I may not lead; Just bugger off and leave me alone!! Encoding vs Encrypting HakunaMatada13-Jul-07 0:22 HakunaMatada 13-Jul-07 0:22  Can someone tell me the difference between Encoding and Encryption? I tried searching high and low but couldn't get any answer. Thanks for your time. --- Hakuna-Matata It means no worries for the rest of your days... It's our problem free, Philosophy "I think my response was 'What idiot dreamed this up?'" -- Mary Ann Davidson, Oracle's chief security officer, in typical blunt manner, remembering her reaction to the company's scheme to brand its databases as "unbreakable." Re: Encoding vs Encrypting SHatchard13-Jul-07 0:59 SHatchard 13-Jul-07 0:59  I am not sure of an exact definition but as far as I am aware encoding is changing the way that the string is displayed, to mask it or change its format but is essentially in a fixed format and easily reversable. Encrypting masks the string with a key of some type (dependent on encryption type) and can usually be decrypted with the provided key. Some encryption cannot be unencrypted, such as MD5, but the same encrypted string can be compared for validation - useful for passwords. Not exactly a dictionary definition i know! Re: Encoding vs Encrypting Paul Conrad13-Jul-07 10:32 Paul Conrad 13-Jul-07 10:32  I'll add that MD5 isn't considered a strong encryption algorithm these days. "Any sort of work in VB6 is bound to provide several WTF moments." - Christian Graus Re: Encoding vs Encrypting CPallini13-Jul-07 2:57 CPallini 13-Jul-07 2:57  Encoding a string has to do with its internal representation. For instance, UTF8 or UNICODE maybe different internal representations of the same string. On the other hand, encryption aims to alter the string in such way that its original content is not recognizable by unauthorized people. Usually encryption imply encoding, usually encoding doens't imply encryption. If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile. Re: Encoding vs Encrypting Luc Pattyn13-Jul-07 10:25 Luc Pattyn 13-Jul-07 10:25  Hi, encoding is the process of mapping a collection of some type1 onto a collection of some type2, for instance you can encode the days of the week into the numbers 1 to 7; and the ASCII character encoding maps the character set we all know to a subset of 8-bit numbers. So it is a representation thing (a one-to-one mapping), often aiming at increasing readability or efficiency. encryption is the process of changing the representation in order to hide the content. the goal is not to make things easier, smaller, more economical; it is to hide the true meaning of things. Luc Pattyn try { [Search CP Articles] [Search CP Forums] [Forum Guidelines] [My Articles] } catch { [Google] } Re: Encoding vs Encrypting MarkB77716-Jul-07 23:16 MarkB777 16-Jul-07 23:16  Wikipedia man!!! Mark Re: Encoding vs Encrypting Sathesh Sakthivel18-Jul-07 0:14 Sathesh Sakthivel 18-Jul-07 0:14  Encrypting a file means that one is altering it in order to conceal its contents. Encoding it means one is altering it because of technical reasons related to transmitting it (e.g., the Morse code). Regards, Satips. Don't walk in front of me, I may not follow; Don't walk behind me, I may not lead; Walk beside me, and just be my friend. - Albert Camus Newton Rapheson [modified] devvvy12-Jul-07 15:15 devvvy 12-Jul-07 15:15  Newton Rapheson ring a bell (Goal Seek function from Excel, that's the Algo they used)? Packaged bug free code anyone? Thanks a bunch. Re: Newton Rapheson cp987612-Jul-07 20:37 cp9876 12-Jul-07 20:37  You give no hint of what language you want, maybe Numerical Recipes is a good place to start - here is the 'c' version: Newton-Raphson Method[^] Peter "Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time." Re: Newton Rapheson devvvy13-Jul-07 1:27 devvvy 13-Jul-07 1:27  right! Numerical Recipes! Left school for sometime totally forget about it!

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