no heap space... need more heap

[anupam.kumar]

hi guys ,

i m kinda stuck with this ..

this is a project euler problem ... the problem is this

The following iterative sequence is defined for the set of positive integers:

n → n/2 (n is even)
n → 3n + 1 (n is odd)

Using the rule above and starting with 13, we generate the following sequence:
13 → 40 → 20 → 10 → 5 → 16 → 8 → 4 → 2 → 1

It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1.

Which starting number, under one million, produces the longest chain?

NOTE: Once the chain starts the terms are allowed to go above one million.

i just went for straightforward bruteforce approach ...

heres my code

public class pro14
{
	public static void main(String args[]) 
	{
		int j=0,pos=0;
                int upperlimit=1000000;
		ArrayList<Integer> temp = new ArrayList<Integer>();
		ArrayList<Integer> longest = new ArrayList<Integer>();
		for(int i=1;i<upperlimit;i++)
	    {
	        
	        temp.add(new Integer(i));
	        j=i;
	        while(j!=1)
	        {
	            if(j%2==0)
	            {
	                j=j/2;       
                   }
                   else
                   {
                        j=3*j+1;
                   }
                
                temp.add(new Integer(j));
               }
            if(longest.size() < temp.size())
            {
                longest.clear();
                for(int k=0;k<temp.size();k++)
                    longest.add(temp.get(k));                
                pos=i;
            }            
            temp.clear();           
       }        
        System.out.println("The starting number that produces longest chain="+pos);    
        for(int i=0;i<longest.size();i++)
            System.out.print(longest.get(i)+"->");
            
    }

	}

the above code works for 100,1000,10000,100000 but not a million ... for example if i change upperlimit variable to 100000 (hundred thousand) i get the output as

The starting number that produces longest chain=77031
77031->231094->115547->346642->173321->519964->259982->129991->389974->194987->584962->292481->877444->438722->219361->658084->329042->164521->493564->246782->123391->370174->185087->555262->277631->832894->416447->1249342->624671->1874014->937007->2811022->1405511->4216534->2108267->6324802->3162401->9487204->4743602->2371801->7115404->3557702->1778851->5336554->2668277->8004832->4002416->2001208->1000604->500302->250151->750454->375227->1125682->562841->1688524->844262->422131->1266394->633197->1899592->949796->474898->237449->712348->356174->178087->534262->267131->801394->400697->1202092->601046->300523->901570->450785->1352356->676178->338089->1014268->507134->253567->760702->380351->1141054->570527->1711582->855791->2567374->1283687->3851062->1925531->5776594->2888297->8664892->4332446->2166223->6498670->3249335->9748006->4874003->14622010->7311005->21933016->10966508->5483254->2741627->8224882->4112441->12337324->6168662->3084331->9252994->4626497->13879492->6939746->3469873->10409620->5204810->2602405->7807216->3903608->1951804->975902->487951->1463854->731927->2195782->1097891->3293674->1646837->4940512->2470256->1235128->617564->308782->154391->463174->231587->694762->347381->1042144->521072->260536->130268->65134->32567->97702->48851->146554->73277->219832->109916->54958->27479->82438->41219->123658->61829->185488->92744->46372->23186->11593->34780->17390->8695->26086->13043->39130->19565->58696->29348->14674->7337->22012->11006->5503->16510->8255->24766->12383->37150->18575->55726->27863->83590->41795->125386->62693->188080->94040->47020->23510->11755->35266->17633->52900->26450->13225->39676->19838->9919->29758->14879->44638->22319->66958->33479->100438->50219->150658->75329->225988->112994->56497->169492->84746->42373->127120->63560->31780->15890->7945->23836->11918->5959->17878->8939->26818->13409->40228->20114->10057->30172->15086->7543->22630->11315->33946->16973->50920->25460->12730->6365->19096->9548->4774->2387->7162->3581->10744->5372->2686->1343->4030->2015->6046->3023->9070->4535->13606->6803->20410->10205->30616->15308->7654->3827->11482->5741->17224->8612->4306->2153->6460->3230->1615->4846->2423->7270->3635->10906->5453->16360->8180->4090->2045->6136->3068->1534->767->2302->1151->3454->1727->5182->2591->7774->3887->11662->5831->17494->8747->26242->13121->39364->19682->9841->29524->14762->7381->22144->11072->5536->2768->1384->692->346->173->520->260->130->65->196->98->49->148->74->37->112->56->28->14->7->22->11->34->17->52->26->13->40->20->10->5->16->8->4->2->1->

so when i try the same for a million i get this

mintoo@mintoo pro14]$ java pro14
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at pro14.main(pro14.java:32)

i have even tried

java -Xms512m -Xmx2048m pro14
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:2772)
	at java.util.Arrays.copyOf(Arrays.java:2746)
	at java.util.ArrayList.ensureCapacity(ArrayList.java:187)
	at java.util.ArrayList.add(ArrayList.java:378)
	at pro14.main(pro14.java:32)
[mintoo@mintoo pro14]$

[anupam.kumar]

i did not need to consider the actual values themselves ... i just needed to consider the length ... i ll print the values to file if at all i need them ... but actually i dont

[JosAH]

i did not need to consider the actual values themselves ... i just needed to consider the length ... i ll print the values to file if at all i need them ... but actually i dont

So don't add them to a list; increment a simple counter instead.

kind regards,

Jos

[anupam.kumar]

:) yea thats what i did :)