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;    }}