leetcode-445-两数相加②

 方法一：栈

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        Stack<Integer> stack1 = new Stack<>();
        Stack<Integer> stack2 = new Stack<>();
        while(l1 != null){
            stack1.push(l1.val);
            l1 = l1.next;
        }
        while(l2 != null){
            stack2.push(l2.val);
            l2 = l2.next;
        }
        int carry = 0;
        ListNode head = null;
        while (!stack1.isEmpty() || !stack2.isEmpty() || carry>0){
            int sum = carry;
            sum += stack1.isEmpty()?0:stack1.pop();
            sum += stack2.isEmpty()?0:stack2.pop();
            ListNode node = new ListNode(sum%10);
            node.next = head;
            head = node;
            carry = sum/10;
        }
        return head;
    }
}