suite_de_collatz_iteration.groovy

def next=[1:1];
def length = [1:1];

def getNext(number) {
    if((number%2)==0) {
        return number/2;
    } else {
        return 3*number+1;
    }
}

def getSequence(numbers, number) {
	def returned = [];
	returned << number;
	if(number!=1) {
		returned.addAll(getSequence(numbers, numbers.get(number)));
	}
	return returned;
}

def getLength(next, length, i) {
	int size = 1;
	int number = i;
	while(number!=1) {
		number = next[number];
		if(length.containsKey(number)) {
			size+=length[number];
			break;
		} else {
			size++;
		}
	}
	return size;
}

long start = System.currentTimeMillis();
def toCompute = [];
def max = 1000000;
toCompute+=1..max;
int index=0;
while(toCompute.size()>0) {
    def current = toCompute.remove(0);
    if(!next.containsKey(current)) {
        next[current]=getNext(current).toInteger();
        if(!next.containsKey(next[current])) {
            toCompute << next[current];
        }
		if(index%100000==0) 
			println "$index th number reached in "+(System.currentTimeMillis()-start)+" ms";
		index++;
    }
}
println "all values computed";

index=0;
for(i in next.keySet()) {
	length[i] = getLength(next, length, i);
		if(index%100000==0) 
			println "$index th length computed in "+(System.currentTimeMillis()-start)+" ms";
		index++;
}

println "max length = "+length.values().max();

long end = System.currentTimeMillis();
println "duration "+((end-start)/1000.0)+" s";