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Author: tech-cow

README.md

@@ -18,3 +18,4 @@ Success is like pregnancy, Everybody congratulates you but nobody knows how many
 |203|[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/#/description) | [Python](./linkedlist/RemoveLinkedListElements.py) | _O(n)_| _O(1)_  | Easy || |
 |206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/#/description) | [Python](./linkedlist/ReverseLinkedList.py) | _O(n)_| _O(1)_  | Easy |CC189| [Video Tutorial](https://www.youtube.com/watch?v=sYcOK51hl-A&t=681s) |
 |234|[Palindrome Linked List](https://leetcode.com/problems/palindrome-linked-list/) | [Python](./linkedlist/palindrome.py) | _O(n)_| _O(1)_  | Easy |CC189| Two Pointers|
+|2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/#/description) | [Python](./linkedlist/addTwoNumbers.py) | _O(n)_| _O(n)_  | Medium |CC189| ||

linkedlist/addTwoNumbers.py

@@ -0,0 +1,73 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# Author: Yu Zhou
+# 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 contain a single digit. Add the two numbers and return it as a linked list.
+# You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+# Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
+# Output: 7 -> 0 -> 8
+
+# ****************
+# Final Solution *
+# ****************
+class Solution(object):
+    def addTwoNumbers(self, n1, n2):
+        """
+        :type l1: ListNode
+        :type l2: ListNode
+        :rtype: ListNode
+        """
+        ret = ListNode(0)
+        temp = ret
+        carry = 0
+        while n1 or n2 or carry:
+            result = carry
+            if n1:
+                result += n1.val
+                n1 = n1.next
+            if n2:
+                result += n2.val
+                n2 = n2.next
+            newNode = ListNode(result % 10)
+            carry = result / 10
+            temp.next = newNode
+            temp = temp.next
+        return ret.next
+
+
+# ***************************************
+# The following code is an fail attempt *
+# ***************************************
+
+class Solution(object):
+    def addTwoNumbers(self, n1, n2):
+        ret = ListNode(0)
+        temp = ret
+        carry = 0
+        while n1 or n2:
+            result = carry
+
+            if n1:
+                result += n1.val
+                n1 = n1.next
+            if n2:
+                result += n2.val
+                n2 = n2.next
+            newNode = ListNode(result % 10)
+            carry = result / 10
+            print newNode.val
+            temp.next = newNode
+        return ret.next
+
+# 代码解析：
+# 首先代码打印不出来，因为忘记了一个重要的步骤
+# 当把Temp.next指向newNode以后，我没有更新Temp本身，所以，temp永远处于
+# ret的位置，所以应该是
+#       temp.next = newNode
+#       temp = temp.next
+
+# 然后代码还是不工作，因为忘记了一个Edge case
+# 当这段代码运行至  n1或者n2的底端，自动就结束了
+# 若是最后两个数相加有一个carry，就会被Truncate掉
+# 所以应该在while里面加一个condition
+#       while n1 or n2 or carry: