longest_collatz_sequence_using_expando.groovy

def numbers=[1:[1]];


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

def getSequence(numbers, number) {
    if(numbers.containsKey(number)) {
        return numbers.get(number);
    } else {
        def next = getNext(number).toInteger();
        def seq = new Expando();
        seq.next = next;
        seq.nextSequence = getSequence(numbers, next);
        seq.number = number;
        seq.toString = {
            return number+ " -> "+nextSequence;
        }
        seq.size = ((seq.nextSequence instanceof Expando) ? seq.nextSequence.size+1 : 2);
        numbers[number]=seq;
        return seq;
    }
}

long start = System.currentTimeMillis();
for(i in 1..1000000) {
    getSequence(numbers, i);
}

max = 0;
numbers.each { k, v->
    if(k>1) {
        if(v.size>max) {
            max = v.size;
        }
    }
}
println "maximum length is $max";
long end = System.currentTimeMillis();
println "duration "+((end-start)/1000.0)+" s";