Problem 660. Find a subset that divides the vector into equal halves

Created by Ned Gulley

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Given a vector x, return the indices to elements that will sum to exactly half of the sum of all elements.

Example:

 Input  x  = [1 2 3 4 5 6 7]
 Output xi = [1 6 7]

because

 sum(x) = 28
 sum(x([1 6 7])) = 14

The answer is not necessarily unique and the order is unimportant. We will just test to make sure that sum(x)/2 is sum(x(xi))

Solve

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2071 Solutions
391 Solvers

Last Solution submitted on Apr 04, 2025

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14 Comments

14 Comments

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AMITAVA BISWAS on 11 Jun 2012

Could you please post the link to ASEE Challenge June 10-13? Thanks!

Ned Gulley on 14 Jun 2012

Amitava, do you mean here? The link is http://www.mathworks.com/matlabcentral/cody/?sort=created+desc&term=group%3A%22ASEE+Challenge%22

Vieniava on 6 Dec 2012

it seems that tests no3 and no4 are incorrectly defined. Ned, check this out please.

Ned Gulley on 7 Dec 2012

@Vieniava, can you be more specific? The tests are the same in all cases. I did verify that Solution 173962 does indeed get an incorrect answer to tests 3 and 4.

Ted on 16 Mar 2013

This was fun

Jean-Marie Sainthillier on 17 Mar 2013

A lot a very beautiful solutions.

J.R.! Menzinger on 18 Nov 2013

What was changed on 5th. November?? :-/

Ned Gulley on 19 Nov 2013

I added a new test. I periodically strengthen test suites to defeat look-up table strategies.

Aryaa Ravieshancar on 2 Feb 2014

I solved this with matlab inbuilt function 'combnk'. Is that not allowed? It gives me the error 'Undefined function' everytime I run my solution.

Ned Gulley on 3 Feb 2014

Aryaa: Your solution looks good. The problem is that combnk is in the Statistics Toolbox, and Cody is designed to use only functions from basic MATLAB.

Hassan Dehghani on 5 Apr 2014

I used random numbers, but couldn't get it. :( (worked fine in my laptop.) :( I guess I haven't completely understood the question. :((

Hassan Dehghani on 7 Apr 2014

why do i get internal server error :(((

Ned Gulley on 8 Apr 2014

Hassan, where are you getting an internal server error? Maybe leave your comment on the solution that has the related error? I'm guessing that your solution relies on randomness, so if you don't get lucky, the answer will time out. You may get lucky on your computer, but not on the Cody server.

John D'Errico on 22 Aug 2016

A basic one liner with intlinprog, but not an option in Cody. :)

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Problem 660. Find a subset that divides the vector into equal halves

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Last 200 Solutions

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Problem 660. Find a subset that divides the vector into equal halves

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Last 200 Solutions

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Problem Recent Solvers391

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