leecode algo2: Add Two Numbers (Java)

leecode algo2: Add Two Numbers

題目：

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

具體實現如下（leetcode 提交通過， Run Time：4ms）：

package algo2;

public class ListNode {
	int val;
	ListNode next;
	ListNode(int x) { val = x; }
}

package algo2;

public class Solution {

	public static void main(String[] args) {
		Solution s = new Solution();
		ListNode l1 = new ListNode(1);
		l1.next = new ListNode(8);
		ListNode l2 = new ListNode(0);
		ListNode sum = s.addTwoNumbers(l1, l2);
		while(sum != null) {
			System.out.print(sum.val + "\t");
			sum = sum.next;
		}
	}

	public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
		ListNode sum = null, tmp = null;
		int carry = 0;
		if(l1 != null && l2 != null) {
			sum = new ListNode((l1.val + l2.val)%10);
			tmp = sum;
			carry = (l1.val + l2.val)/10;
			l1 = l1.next;
			l2 = l2.next;
		}
		while(l1 != null && l2 != null) {
			tmp.next = new ListNode((l1.val + l2.val + carry)%10);
			carry = (l1.val + l2.val + carry)/10;
			l1 = l1.next;
			l2 = l2.next;
			tmp = tmp.next;
		}
		while(l1 == null && l2 != null) {
			tmp.next = new ListNode((l2.val + carry)%10);
			carry = (l2.val + carry)/10;
			l2 = l2.next;
			tmp = tmp.next;
		}
		while(l1 != null && l2 == null) {
			tmp.next = new ListNode((l1.val + carry)%10);
			carry = (l1.val + carry)/10;
			l1 = l1.next;
			tmp = tmp.next;
		}
		if(carry != 0) {
			tmp.next = new ListNode(carry);
		}
		return sum;
	}
}