2. Add Two Numbers

2. Add Two Numbers

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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

My solution:

• 把两个lists的每一个node(!= null)记下并相加

• 用carry 记录进位

• 如果最后carry不为0，多加一个ListNode(1)

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

        ListNode dummy = new ListNode(0);
        ListNode p = l1, q = l2, curr = dummy;
        int carry = 0;

        while (p != null || q != null) {
            int x = p == null? 0 : p.val;
            int y = q == null? 0 : q.val;
            int sum = x + y + carry;
            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(1); 

        return dummy.next;

    }
}