【leetcode】002 Add Two Numbers

You are given two linked lists representing two non-negative numbers. 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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

【题意解析】从两个非负倒序储存元素链表中提取出两个数字相加，并将得到的结果转换为倒序储存的链表。

【解题思路】题目中提到是倒序存储，所有上述既为342+465=807。单链表，我们从题意很容易得到解题思路：用两个指针分别同步遍历两个链表将对应的节点值相加后，再加上前一对节点的进位值（初值为0）。用得到的新值模10后建立节点，并计算下一个节点的进位值。注意，若最后进位值不为0则需要增加一个尾节点。

AC CODE:

class Solution {
public:
  ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
    ListNode *lstres =NULL, *lstid = NULL, *pt1=l1, *pt2=l2;
    int forward = 0;
    while (pt1 || pt2)
    {
      int t = forward;
      if (pt1) { t += pt1->val; pt1 = pt1->next; }
      if (pt2) { t += pt2->val; pt2 = pt2->next; }
      if (!lstres)
      {
        lstres = new ListNode(t%10);
        lstid = lstres;
      }else
      {
        lstid->next = new ListNode(t%10);
        lstid = lstid->next;
      }
      forward = t/10;
    }
    if (forward)
      lstid->next = new ListNode(forward);
    return lstres;
  }
};

题目链接：https://oj.leetcode.com/problems/add-two-numbers/

leetcode全套习题code下载：

                               github：https://github.com/huoyao/TL_letcd