Add Two Numbers

06/17/2016 Linked List Math

Question
Solution

Question

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

Solution

Result: Accepted Time: 20ms

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        ListNode  head(0);
        ListNode * tail = &head;
        int carry = 0;
        while(l1 || l2 )
        {
            if(l1)
                carry += l1 -> val, l1 = l1->next;
            if(l2)
                carry += l2 -> val, l2 = l2->next;
            tail->next =  new ListNode(carry%10);
            tail = tail->next;
            carry /= 10;
        }
        if(carry)
            tail->next = new ListNode(carry);
        return head.next;
    }
};

Complexity Analytics

Time Complexity: $O(max(m,n))$
Space Complexity: $O(max(m,n))$