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

LeetCode-Add Two Numbers

C++:
/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(l1==NULL&&l2==NULL) return NULL;
        ListNode *head=NULL;
        ListNode *pre=NULL;
        int flag=0;
        while(l1&&l2){
            ListNode *cur=new ListNode((l1->val+l2->val+flag)%10);
            flag=(l1->val+l2->val+flag)/10;
            if(head==NULL) head=cur;
            else pre->next=cur;
            pre=cur;
            l1=l1->next;
            l2=l2->next;
        }
        while(l1){
            ListNode *cur=new ListNode((l1->val+flag)%10);
            flag=(l1->val+flag)/10;
            if(head==NULL) head=cur;
            else pre->next=cur;
            pre=cur;
            l1=l1->next;
        }
        while(l2){
            ListNode *cur=new ListNode((l2->val+flag)%10);
            flag=(l2->val+flag)/10;
            if(head==NULL) head=cur;
            else pre->next=cur;
            pre=cur;
            l2=l2->next;
        }
        if(flag){
            ListNode *cur=new ListNode(flag);
            pre->next=cur;
            pre=cur;
        }
        return head;
    }
};
Java:
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(l1==null&&l2==null) return null;
        ListNode head=null;
        ListNode pre=null;
        int flag=0;
        while(l1!=null&&l2!=null){
            ListNode cur=new ListNode((l1.val+l2.val+flag)%10);
            flag=(l1.val+l2.val+flag)/10;
            if(head==null) head=cur;
            else pre.next=cur;
            pre=cur;
            l1=l1.next;
            l2=l2.next;
        }
        while(l1!=null){
            ListNode cur=new ListNode((l1.val+flag)%10);
            flag=(l1.val+flag)/10;
            if(head==null) head=cur;
            else pre.next=cur;
            pre=cur;
            l1=l1.next;
        }
        while(l2!=null){
            ListNode cur=new ListNode((l2.val+flag)%10);
            flag=(l2.val+flag)/10;
            if(head==null) head=cur;
            else pre.next=cur;
            pre=cur;
            l2=l2.next;
        }
        if(flag>0){
            ListNode cur=new ListNode(flag);
            pre.next=cur;
            pre=cur;
        }
        return head;
    }
}