NOTE: This problem is generated by LeetCode. TakeTheNotes has given only solution for educational purpose.


Problem Name: Add Two Numbers

Description: 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 contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]

Example 2:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

Constraints:

  • The number of nodes in each linked list is in the range [1, 100].
  • 0 <= Node.val <= 9
  • It is guaranteed that the list represents a number that does not have leading zeros.

Solution:

struct ListNode* addTwoNumbers(struct ListNode* l1, struct ListNode* l2){

    struct ListNode* retVal = (struct ListNode *)calloc(1, sizeof(struct ListNode));
    if(retVal == NULL)
    {
        return NULL;
    }

    struct ListNode* head = retVal;
    char carry = 0;

    while(1)
    {        
        int sum = 0;

        if(l1 != NULL)
        {
            sum = l1->val;
            l1 = l1->next;
        }

        if(l2 != NULL)
        {
            sum += l2->val;
            l2 = l2->next;
        }

        sum += carry;

        carry = sum/10;
        retVal->val = sum%10;

        if(l1 == NULL && l2 == NULL)
        {
            break;
        }


        retVal->next = (struct ListNode *)calloc(1, sizeof(struct ListNode));
        if(retVal->next == NULL)
        {
            //not able to allocate memory. So returning
            return head;
        }
        
        retVal = retVal->next;
    }

    if(carry)
    {
        retVal->next = (struct ListNode *)calloc(1, sizeof(struct ListNode));
        if(retVal->next == NULL)
        {
            //not able to allocate memory. So returning
            return head;
        }

        retVal = retVal->next;
        retVal->val = carry;
    }

    return head;
}