[LeetCode] Add Two Numbers

[Problem]

You are given two linked lists representing two non-negativenumbers. The digits are stored in reverse order and each of theirnodes contain a single digit. Add the two numbers and return it asa linked list.

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

[Analysis]
简单题，类似于两个排序链表的合并，注意最后的进位。

[Solution]

class Solution {
public:
    ListNode *addTwoNumbers(ListNode *l1, ListNode *l2) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        ListNode *res = NULL;
        ListNode *p = NULL;
        int sum = 0, add = 0;
        while(true){
            // end
            if(l1 == NULL && l2 == NULL){
                break;
            }

            // add two list
            sum = add;
            if(l1 != NULL){
                sum += l1 -> val;
                l1 = l1 -> next;
            }
            if(l2 != NULL){
                sum += l2 -> val;
                l2 = l2 -> next;
            }
            add = sum / 10;
            sum = sum % 10;
            ListNode *node = new ListNode(sum);
           
            // append to result
            if(res == NULL){
                res = node;
            }
            else{
                p = res;
                while(p -> next != NULL){
                    p = p -> next;
                }
                p -> next = node;
            }
        }

        // be careful the last carry
        if(add > 0){
            ListNode *node = new ListNode(add);
   
            // append to result
            if(res == NULL){
                res = node;
            }
            else{
                p = res;
                while(p -> next != NULL){
                    p = p -> next;
                }
                p -> next = node;
            }
        }
        return res;
    }
};

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