2. Add Two Numbers

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */


struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2){
    struct ListNode* result = (struct ListNode*)malloc(sizeof(struct ListNode)*1);
    result->val = 0;
    result->next = NULL;
    struct ListNode* p = result;
    p = result;
    int add = 0;
    int sum = 0;
    while(l1 && l2)
    {
        sum = add + l1->val + l2->val;
        result->next = (struct ListNode*)malloc(sizeof(struct ListNode));
        result->next->val = sum % 10;
        result->next->next = NULL;
        add = sum / 10;
        result = result->next;
        l1 = l1->next;
        l2 = l2->next;
    }

    while(l1)
    {
        sum = add + l1->val;
        result->next = (struct ListNode*)malloc(sizeof(struct ListNode));
        result->next->val = sum % 10;
        result->next->next = NULL;
        add = sum / 10;
        result = result->next;
        l1 = l1->next;
    }

    while(l2)
    {
        sum = add + l2->val;
        result->next = (struct ListNode*)malloc(sizeof(struct ListNode));
        result->next->val = sum % 10;
        result->next->next = NULL;
        add = sum / 10;
        result = result->next;
        l2 = l2->next;
    }

    if(add)
    {
        result->next = (struct ListNode*)malloc(sizeof(struct ListNode));
        result->next->val = add;
        result->next->next = NULL;
        result = result->next;  
    }
    struct ListNode* q = p;
    p = p->next;
    free(q);

    return p;
}