/**
 * An IntList is a list of ints.
 */
public class IntList {
    private ConsCell start; // first in the list or null

    /**
     * Construct a new IntList given its first ConsCell.
     * @param s the first ConsCell in the list or null
     */
    private IntList(ConsCell s) {
        start = s;
    }

    private static final IntList NIL = new IntList(null);

    /**
     * Return an empty IntList.
     */
    public static IntList getEmpty(){
        return NIL;
    }

    /**
     * Return an IntList containing the given elements.
     * @param elements the ints to go in the list
     */
    public static IntList make(int... elements){
        IntList list = IntList.getEmpty();
        for(int i = elements.length - 1; i >= 0; i--){
            list = list.cons(elements[i]);
        }
        return list;
    }

    /**
     * Cons the given element h onto us and return the
     * resulting IntList.
     * @param h the head int for the new list
     * @return the IntList with head h and us for a tail
     */
    public IntList cons (int h) {
        return new IntList(new ConsCell(h,start));
    }

    /**
     * Get our length.
     * @return our int length
     */
    public int length() {
        int len = 0;
        ConsCell cell = start;
        while (cell != null) { // while not at end of list
            len++;
            cell = cell.getTail();
        }
        return len;
    }

    /**
     * Print ourself to System.out.
     */
    public void print() {
        System.out.print("[");
        ConsCell a = start;
        while (a != null) {
            System.out.print(a.getHead());
            a = a.getTail();
            if (a != null) System.out.print(",");
        }
        System.out.println("]");
    }

    /**
     * A ConsCell is an element in a linked list of
     * ints.
     */
    private static class ConsCell {
        private int head; // the first item in the list
        private ConsCell tail; // rest of the list or null

        /** 
         * Construct a new ConsCell given its head and tail.
         * @param h the int contents of this cell
         * @param t the next ConsCell in the list or null
         */
        public ConsCell(int h, ConsCell t) {
            head = h;
            tail = t;
        }
        /**
         * Accessor for the head of this ConsCell.
         * @return the int contents of this cell
         */
        public int getHead() {
            return head;
        }

        /**
         * Accessor for the tail of this ConsCell.
         * @return the next ConsCell in the list or null
         */
        public ConsCell getTail() {
            return tail;
        }
    }

}