2. Add Two Numbers

# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: def addTwoNumbers(self, l1, l2): """ :type l1: ListNode :type l2: ListNode :rtype: ListNode """ ListNode dummy1, dummy2, dummy3, res_head dummy1 = l1 dummy2 = l2 dummy3 = res_head carry = 0 while(dummy1 != None and dummy2 != None): curr_val = dummy1.val + dummy2.val + carry carry = 0 # clean carry if curr_val >= 10: curr_val -= 10 carry = 1 curr_node = ListNode(curr_val) # add a new node dummy3.next = curr_node # append the node to the linkedlist dummy3 = curr_node dummy1 = dummy1.next dummy2 = dummy2.next # move the dummy head one step down if dummy1 == None: # now list one is finished while(dummy2 != None): curr_val = dummy2.val + carry carry = 0 if curr_val >= 10: curr_val -= 10 carry = 1 curr_node = ListNode(curr_val) dummy3 = curr_node