20170720 - Add Two Numbers - Meduim

/**
 * 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) {
        ListNode* i1 = l1;
        ListNode* i2 = l2;
        ListNode* head;
        ListNode* add;
        ListNode* before;
        int m = 0;

        add = new ListNode(0);
        if (i1 != NULL) add->val = add->val + i1->val;
        if (i2 != NULL) add->val = add->val + i2->val;

        if (add->val >= 10)
        {
           m = (int)( add->val / 10 ) ;
           add->val = add->val % 10;
        }    
        
        head = add;
        
        if (i1 != NULL) i1 = i1->next;
        if (i2 != NULL) i2 = i2->next;        
        
        while(i1 != NULL || i2 != NULL)
        {
            before = add;

            add = new ListNode(m);
           
            if (i1 != NULL) add->val = add->val + i1->val;
            if (i2 != NULL) add->val = add->val + i2->val;
            
            m = 0;
            if (add->val >= 10)
            {
                m = (int)( add->val / 10 ) ;
                add->val = add->val % 10;
            }    
            
            before->next = add;

            if (i1 != NULL) i1 = i1->next;
            if (i2 != NULL) i2 = i2->next;

        };
        
        if (m != 0)
        {
            before = add;
            add = new ListNode(m);
            before->next = add;
        }
        add->next = NULL;
        return head;
    }
};