4offer

Leetcode------string.cpp

/*******************************************************************
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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
*******************************************************************/
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        if(l1==nullptr && l2==nullptr)
            return nullptr;
        ListNode* head = new ListNode(0);
        ListNode* ptr = head;
        ptr->next = nullptr;
        int carry = 0;
        while(l1 != nullptr || l2 != nullptr){
            int sum = 0;
            sum += carry;
            if(l1 != nullptr){
                sum += l1->val;
                l1 = l1->next;
            }
            if(l2!= nullptr){
                sum += l2->val;
                l2 = l2->next;
            }
            ListNode* temp = new ListNode(sum%10);
            carry = sum/10;
            ptr->next = temp;
            ptr = ptr->next;
        }
        if(carry == 1){
            ListNode* temp = new ListNode(1);
            ptr->next = temp;
            ptr = ptr->next;
        }
        ptr->next = nullptr;
        return head->next;
    }
};