AddTwoNumbers.java

/**
 * AddTwoNumbers
 * 
 * You are given two non-empty linked lists representing two non-negative integers.
 * The digits are stored in reverse order and each of their nodes contain a single digit.
 * Add the two numbers and return it as a linked list.
 * You may assume the two numbers do not contain any leading zero, except the number 0 itself.
 * 
 * Compile and Run
 * javac -cp .:../common AddTwoNumbers.java 
 * java -cp .:../common AddTwoNumbers
 */
public class AddTwoNumbers {

    public ListNode addTowNumbers(ListNode l1, ListNode l2) {
        ListNode dummyNode = new ListNode(0);
        ListNode p = l1, q = l2, curr = dummyNode;
        int carry = 0;
        while (p != null || q != null) {
            int x = (p != null) ? p.value : 0;
            int y = (q != null) ? q.value : 0;
            int sum = carry + x + y;
            carry = sum / 10;
            curr.next = new ListNode(sum % 10);
            curr = curr.next;
            if (p != null) p = p.next;
            if (q != null) q = q.next;
        }
        if (carry > 0) {
            curr.next = new ListNode(carry);
        }

        return dummyNode.next;
    }

    public static void main(String[] args) {
        ListNode l1 = new ListNode(2);
        l1.next = new ListNode(4);
        l1.next.next = new ListNode(3);

        ListNode l2 = new ListNode(5);
        l2.next = new ListNode(6);
        l2.next.next = new ListNode(4);

        ListNode newListNode = new AddTwoNumbers().addTowNumbers(l1, l2);

        while (newListNode != null) {
            System.out.print(newListNode.value + " ");
            newListNode = newListNode.next;
        }
    }

}