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Summation of `multiples of 5` which sums to a given target

Deepak Lal
Ranch Hand

Joined: Jul 01, 2008
Posts: 507

Write a java function such that given an array of ints, is it possible to choose a group of some of the ints, such that the group sums to the given target with these additional constraints: all multiples of 5 in the array must be included in the group. If the value immediately following a multiple of 5 is 1, it must not be chosen.

groupSum5(0, {2, 5, 10, 4}, 19) => true
groupSum5(0, {2, 5, 10, 4}, 17) => true
groupSum5(0, {2, 5, 10, 4}, 12) => false

I have written the partial code as below but is not working properly.could you check what might be wrong.

Im unable to proceed further.Code fix provided will be appreciated.>

When The Going Gets Tougher,The Tougher gets Going
fred rosenberger
lowercase baba

Joined: Oct 02, 2003
Posts: 11164

What exactly do you mean by "Not working properly"? Please tell us the details. What have you tried that works, what have you tried that doesn't work, etc?

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Joanne Neal

Joined: Aug 05, 2005
Posts: 3431
Two problems that I can see

1. At line 8 and 12 you return true if the target has been matched, yet this doesn't allow for numbers later in the list being multiples of 5. You need to get the sum of all your multiples of 5 before you even begin looking at the other numbers.

2. Line 13 will only skip the value 5, not all multiples of 5.

Fix those and then if you still have problems, see Fred's post

Deepak Lal
Ranch Hand

Joined: Jul 01, 2008
Posts: 507

I have refined my code as below

All the test cases are still failing.could you help me out to fix this piece of code.>
Joanne Neal

Joined: Aug 05, 2005
Posts: 3431
You still haven't done anything about the first problem I mentioned. You need a separate loop that sums all the values that are multiples of 5. If this sum is greater than the target value you can then immediately return false without checking the other numbers. If not you then use it as a base value when checking the other numbers.

What are you doing on line 7 ? You only increase the value of start if its current value is a multiple of 5.

Lines 10 and 11 can be replaced by
Marius Zilenas

Joined: Jun 04, 2014
Posts: 1

This is recursive solution for the given problem of summing ints with 5's multiples required and 1's excluded if after 5's multiples.
Campbell Ritchie

Joined: Oct 13, 2005
Posts: 38044
Welcome to the Ranch and thank you for that solution.
Mike. J. Thompson
Ranch Hand

Joined: Apr 17, 2014
Posts: 229
The question says you need to decide if any [i]subset[i] of the applicable numbers sum to the target value.

It is not sufficient to sum the numbers in sequence until the sum is greater than or equal to the target value because this will not check all of the subsets. You need to:

* Find the set of numbers that match the rules.
* Create a list of all non-empty sub-sets of those numbers.
* Sum each subset until you find one that sums to the target value.
Don't get me started about those stupid light bulbs.
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