addListSum

addListSum

Given two linked lists, each element of the lists is a integer. Write a
function to return a new list, which is the “sum” of the given two lists.
Part a. Given input (7->1->6) + (5->9->2), output 2->1->9.

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解法：前节点的解不依赖靠后节点，因此顺序遍历求解即可

class Solution {public:    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {        ListNode dummy(0);        ListNode* p = &dummy;        int cn = 0;        while (l1 || l2) {            int val = cn + (l1 ? l1->val : 0) + (l2 ? l2->val : 0);            cn = val / 10;    // carry in 进位            val = val % 10;   // sum            p->next = new ListNode(val);            p = p->next;            if(l1) {                l1 = l1->next;            }            if(l2) {                l2 = l2->next;            }        }        // 保存最后一个进位        if(cn != 0) {            p->next = new ListNode(cn);            p = p->next;        }        return dummy.next;    }};