力扣 面试题 02.05. 链表求和

一开始想把两个整数都求出来再求和，但是这样做是会超出数字长度限制的

模拟加法进位的过程就可以了

class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        int t = 0;
        ListNode a = new ListNode(0);
        ListNode ind = a;
        while(l1 != null ||l2 != null){
            if(l1 != null)
                t += l1.val;
            if(l2 != null)
                t += l2.val;
            ind.next = new ListNode(t % 10);
            ind = ind.next;
            t /= 10;
            if(l1 != null)
                l1 = l1.next;
            if(l2 != null)
                l2 = l2.next;
        }
        if(t != 0)
            ind.next = new ListNode(t);
        return a.next;
    }
}