LeetCode-2. Add Two Numbers

​​https://leetcode.com/problems/add-two-numbers/description/​​

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

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

题解：

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
  int num1 = 0, num2 = 0, weight1 = 0, weight2 = 0;
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
      ListNode *p = new ListNode(0);
      ListNode *head = p;
      int flag_1 = 0;
      int flag_2 = 0;
      int carry = 0;
      bool first = true;
      while(true){
        int sum_1, sum_2;
        if(l1 != NULL){
          sum_1 = l1->val;
          l1 = l1->next;
        }
        else{
          sum_1 = 0;
          flag_1 = 1;
        }
        if(l2 != NULL){
          sum_2 = l2->val;
          l2 = l2->next;
        }
        else{
          sum_2 = 0;
          flag_2 = 1;
        }
        int sum = sum_1 + sum_2 + carry;
        if(flag_1 == 1 && flag_2 == 1 && carry == 0){
          break;
        }
        else if(flag_1 == 1 && flag_2 == 1 && carry == 1){
          p->next = new ListNode(sum);
          p = p->next;
          break;
        }
        if(sum >= 10){
          sum -= 10;
          carry = 1;
        }
        else{
          carry = 0;
        }
        if(first == true){
          p->val = sum;
          first = false;
        }
        else{
          p->next = new ListNode(sum);
          p = p->next;
        }
      }
      return head;
    }
};