add two numbers

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example:

1
2
3

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

大概题意就是两个链表，逆序访问生成两个数求这个两个数的和，再逆序构建个链表。


 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class  {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode sum = new ListNode(-1);
        ListNode cur = sum;
        int flag = 0;
        while(l1 != null || l2 != null){
            int d1 = l1 == null ? 0 : l1.val;
            int d2 = l2 == null ? 0 : l2.val;
            int summ = d1 + d2 + flag;
            flag = summ >= 10 ? 1 : 0;
            cur.next = new ListNode(summ%10);
            cur = cur.next;
            if(l1 != null ) l1 = l1.next;
            if(l2 != null ) l2 = l2.next;
        }
        if(flag == 1) cur.next = new ListNode(1);
        return sum.next;
    }
}

add two numbers

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