algorithm_linked_list_add_two_numbers

algorithm_linked_list_add_two_numbers.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        if (l1 == null && l2 == null) return null;
        else if (l1 == null) return l2;
        else if (l2 == null) return l1;
        
        ListNode dummyHead = new ListNode(0);
        ListNode curNode   = dummyHead;
        int co  = 0; // carry-over from previous nodes
        while (l1 != null || l2 != null) {
            int sum = 0;
            
            if (l1 != null) {
                sum += l1.val;
                l1 = l1.next;
            }
            if (l2 != null) {
                sum += l2.val;
                l2 = l2.next;
            }
            sum += co;
            
            co   = sum / 10;
            sum %= 10;
            
            curNode.next = new ListNode(sum);
            curNode = curNode.next;
        }
        
        if (co == 1) curNode.next = new ListNode(1);
        return dummyHead.next;
    }
}

algorithm_linked_list_add_two_numbers.py

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        dummyHead = ListNode(0);
        curNode = dummyHead
        
        if not l1 and not l2: return None
        elif not l1:          return l2
        elif not l2:          return l1
        
        co = 0 # carry over from the previous node
        while l1 or l2:
            sum = 0
            if l1:
                sum += l1.val
                l1 = l1.next
            if l2:
                sum += l2.val
                l2 = l2.next
                
            sum += co
            co  = sum / 10
            sum = sum % 10
            
            curNode.next = ListNode(sum)
            curNode = curNode.next
        
        if co == 1:
            curNode.next = ListNode(1)
        
        return dummyHead.next