It looks like you're new here. If you want to get involved, click one of these buttons!

- 140.4K All Categories
- 104.3K Programming Languages
- 6.3K Assembler Developer
- 1.8K Basic
- 39.7K C and C++
- 4.2K C#
- 7.9K Delphi and Kylix
- 4 Haskell
- 9.6K Java
- 4.1K Pascal
- 1.3K Perl
- 1.9K PHP
- 503 Python
- 47 Ruby
- 4.3K VB.NET
- 1.6K VBA
- 20.8K Visual Basic
- 2.6K Game programming
- 308 Console programming
- 88 DirectX Game dev
- 1 Minecraft
- 108 Newbie Game Programmers
- 2 Oculus Rift
- 8.9K Applications
- 1.8K Computer Graphics
- 726 Computer Hardware
- 3.4K Database & SQL
- 520 Electronics development
- 1.6K Matlab
- 627 Sound & Music
- 254 XML Development
- 3.2K Classifieds
- 189 Co-operative Projects
- 171 For sale
- 189 FreeLance Software City
- 1.9K Jobs Available
- 598 Jobs Wanted
- 199 Wanted
- 2.9K Microsoft .NET
- 1.7K ASP.NET
- 1.1K .NET General
- 2.9K Miscellaneous
- 3 Join the Team
- 2 User Profiles
- 352 Comments on this site
- 56 Computer Emulators
- 1.7K General programming
- 136 New programming languages
- 598 Off topic board
- 159 Mobile & Wireless
- 33 Android
- 124 Palm Pilot
- 334 Multimedia
- 151 Demo programming
- 183 MP3 programming
- 0 Bash scripts
- 15 Cloud Computing
- 52 FreeBSD
- 1.7K LINUX programming
- 364 MS-DOS
- 0 Shell scripting
- 318 Windows CE & Pocket PC
- 4.1K Windows programming
- 877 Software Development
- 401 Algorithms
- 67 Object Orientation
- 82 Project Management
- 88 Quality & Testing
- 232 Security
- 7.5K WEB-Development
- 1.8K Active Server Pages
- 61 AJAX
- 2 Bootstrap Themes
- 55 CGI Development
- 19 ColdFusion
- 222 Flash development
- 1.4K HTML & WEB-Design
- 1.4K Internet Development
- 2.2K JavaScript
- 33 JQuery
- 283 WEB Servers
- 107 WEB-Services / SOAP

Welcome to the new platform of Programmer's Heaven! We apologize for the inconvenience caused, if you visited us from a broken link of the previous version. The main reason to move to a new platform is to provide more effective and collaborative experience to you all. Please feel free to experience the new platform and use its exciting features. Contact us for any issue that you need to get clarified. We are more than happy to help you.

lachupacabra
Posts: **1**Member

in Algorithms

Hi!

I got a little problem with this excercise from Introduction to Algorithms (Cormen et al.).

Given a set S of n integers, and an integer x, describe an algorithm of time complexity n*lg(n) which finds if sum of any two elements from S are equal to x.

Examining every pair gives n*n algorithm, which is not what I want.

I think a merge-sort like algorithm could be used, but have no idea how to check if there are two such elements in two subsets (the merge step) in linear time. But maybe the whole idea is wrong. If someone can give any hints on this, I'd appreciate it =)

Oh. My second idea is a 2*n*lg(n) algorithm given below.

merge-sort(S) // takes n*lg(n)

for each y in S: // n times

r = x - y

binary-search(S, r) // takes at most lg(n)

if found then return

If anyone knows a better (faster) solution please let me know.

regards

LaChupacabra

I got a little problem with this excercise from Introduction to Algorithms (Cormen et al.).

Given a set S of n integers, and an integer x, describe an algorithm of time complexity n*lg(n) which finds if sum of any two elements from S are equal to x.

Examining every pair gives n*n algorithm, which is not what I want.

I think a merge-sort like algorithm could be used, but have no idea how to check if there are two such elements in two subsets (the merge step) in linear time. But maybe the whole idea is wrong. If someone can give any hints on this, I'd appreciate it =)

Oh. My second idea is a 2*n*lg(n) algorithm given below.

merge-sort(S) // takes n*lg(n)

for each y in S: // n times

r = x - y

binary-search(S, r) // takes at most lg(n)

if found then return

If anyone knows a better (faster) solution please let me know.

regards

LaChupacabra

About & Contact / Terms of use / Privacy statement / Publisher: Lars Hagelin

Programmers Heaven articles / Programmers Heaven files / Programmers Heaven uploaded content / Programmers Heaven C Sharp ebook / Operated by CommunityHeaven LLC

© 1997-2013 Programmersheaven.com - All rights reserved.