feat(leetcode): add No.2

Author: mickey0524

2.Add-Two-Numbers.py

@@ -0,0 +1,60 @@
+# https://leetcode.com/problems/add-two-numbers/
+#
+# algorithms
+# Medium (31.07%)
+# Total Accepted:    864,234
+# Total Submissions: 2,781,507
+
+
+# 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
+        """
+        if not l1:
+            return l2
+        if not l2:
+            return l1
+        
+        res = l1
+        pre = None
+        
+        carry = 0
+        while l1 and l2:
+            l1.val = l1.val + l2.val + carry
+            if l1.val >= 10:
+                carry = 1
+                l1.val -= 10
+            else:
+                carry = 0
+            pre = l1
+            l1 = l1.next
+            l2 = l2.next
+        
+        if l2:
+            pre.next = l2
+            l1 = l2
+        
+        while l1:
+            l1.val += carry
+            if l1.val >= 10:
+                carry = 1
+                l1.val -= 10
+            else:
+                carry = 0
+            pre = l1
+            l1 = l1.next
+        
+        if carry == 1:
+            pre.next = ListNode(1)
+        
+        return res
+