a Programmer's blog

import java.util.HashMap;
import java.util.Map;

class runner
{
	static HashMap cache = new HashMap();
	public static void mergeCache(HashMap minicache){
		cache.putAll(minicache);
	}
	public static long calc(long n){
		if(n%2 == 0)
			return n/2;
		else
			return 3*n+1;
	}
	public static void main (String[] args) throws java.lang.Exception
	{
		long time = System.currentTimeMillis();
		long lrgLen = 0, lrgNum = 0; 
		for(int i=1; i<1000000; i++){
			HashMap minicache = new HashMap();
			
			long val = i, counter = 1;
			while(val != 1){
				//Check cache
				if(cache.containsKey(val)){
					Integer cachedVal = cache.get(val);
					//update all values in minicache
					for (Map.Entry entry : minicache.entrySet()){
						entry.setValue(entry.getValue()+cachedVal);
					}
					counter += cachedVal;
					break;
				}
				val = calc(val);
				
				//update all values in minicache
				for (Map.Entry entry : minicache.entrySet()){
					entry.setValue(entry.getValue()+1);
				}
				minicache.put(val, 1);
				counter ++;
			}
			
			mergeCache(minicache);
			
			if(counter > lrgLen){
				lrgLen = counter; lrgNum = i;
			}
			
			//System.out.println("cachesize: "+cache.size());
		}
		System.out.println("i: "+lrgNum+" len: "+lrgLen+" time: "+(System.currentTimeMillis() - time));
	}
}