題目 2. Add Two Numbers，單純的將兩個鏈接做相加。須注意的是進位而已。
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode() {}
* ListNode(int val) { this.val = val; }
* ListNode(int val, ListNode next) { this.val = val; this.next = next; }
* }
*/
class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
int carry = 0;
ListNode dummy = new ListNode(0);
ListNode cur = dummy;
int l1Val = 0;
int l2Val = 0;
int sum = 0;
while (l1 != null || l2 != null){
if (l1 == null) {
l1Val = 0;
} else {
l1Val = l1.val;
}
if (l2 == null) {
l2Val = 0;
} else {
l2Val = l2.val;
}
sum = carry + l1Val + l2Val;
carry = sum / 10;
cur.next = new ListNode(sum%10);
cur = cur.next;
if (l1 != null){
l1 = l1.next;
}
if (l2 != null){
l2 = l2.next;
}
}
if (carry == 1){
cur.next = new ListNode(1);
}
return dummy.next;
}
}