Copy linked list which has second link to a random node

def source = [[data: '1', rand: 2], [data: '2', rand: 1], [data: '3', rand: 0]]

class List {

    Node head

    class Node {

        static int glob_id;

        public Node() {
            this.id = glob_id++;
        }

        def id
        def next
        def rand
        def data

        String toString() {
            "[id=${id}: data=${data}]"
        }
    }
}

def create_list(source) {

    List list = new List()

    List.Node tail

    source.each {
        List.Node node = [data: it.data, rand: it.rand] as List.Node

        if (! list.head) {
            list.head = node
        }

        if (! tail) {
            tail = node
        } else {
            tail.next = node
            tail = node
        }
        it << ['node':node]
    }

    source.each {
        it.node.rand = source[it.rand].node
    }

    return list
}

List list = create_list(source)

def print_list(list) {

    List.Node node = list.head
    while (node) {
        println "Node: ${node}, Rand: ${node.rand}"
        node = node.next
    }
}

def copy_list(origin) {

    List copy = new List()

    List.Node copy_tail

    //First pass
    List.Node node = origin.head
    while (node) {

        List.Node copy_node = [data: node.data, rand: node.rand] as List.Node

        next_node = node.next
        node.next = copy_node

        if (! copy.head) {
            copy.head = copy_node
        }

        if (! copy_tail) {
            copy_tail = copy_node
        } else {
            copy_tail.next = copy_node
            copy_tail = copy_node
        }
        node = next_node
    }

    //Second pass
    node = origin.head
    while (node) {
        node.rand = node.rand.next
        node = node.next
    }
    return copy
}

println "\nInitial list:"
print_list(list)

println "\nCopy list:"
print_list(copy_list(list))