C/leetcode/src/2.c

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

struct ListNode *addTwoNumbers(struct ListNode *l1, struct ListNode *l2)
{
    struct ListNode *head = NULL;
    struct ListNode *walk = NULL;
    struct ListNode *tmp = NULL;

    int carry = 0;
    int val1 = 0;
    int val2 = 0;
    int val = 0;

    while (l1 != NULL || l2 != NULL || carry)
    {
        val1 = 0;
        val2 = 0;
        val = 0;

        if (l1)
        {
            val1 = l1->val;
            l1 = l1->next;
        }

        if (l2)
        {
            val2 = l2->val;
            l2 = l2->next;
        }

        val = carry + val1 + val2;
        carry = val / 10;

        tmp = malloc(sizeof(struct ListNode));
        tmp->val = val % 10;
        tmp->next = NULL;

        if (!head)
        {
            head = walk = tmp;
        }
        else
        {
            walk->next = tmp;
            walk = walk->next;
        }
    }

    return head;
}