leetcode 2. Add Two Numbers

/**
* Definition for singly-linked list.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
int len1 = 0, len2 = 0;
for(ListNode p = l1; p != null; p = p.next, len1++);
for(ListNode p = l2; p != null; p = p.next, len2++);
if(len1 > len2) {
ListNode t = l2;
while(t.next != null) t = t.next;
for(int i = len2; i < len1; i++) {
t.next = new ListNode(0);
t = t.next;
}
}
else {
ListNode t = l1;
while(t.next != null) t = t.next;
for(int i = len1; i < len2; i++) {
t.next = new ListNode(0);
t = t.next;
}
}
ListNode ans = new ListNode(l1.val + l2.val), head;
head = ans;
for(l1 = l1.next, l2 = l2.next; l1 != null && l2 != null; l1 = l1.next, l2 = l2.next) {
ans.next = new ListNode(l1.val + l2.val);
ans = ans.next;
}
for(ListNode p = head; p != null; p = p.next) {
if(p.val >= 10) {
p.val %= 10;
if(p.next != null) p.next.val++;
else p.next = new ListNode(1);
}
}
return head;
}
}