no message

Author: Chris Wu

problems/add-two-numbers-ii.py

@@ -0,0 +1,62 @@
+"""
+First, if you haven't done the [first problem](https://leetcode.com/problems/add-two-numbers/) please do it first. And here is its [answer](https://leetcode.com/problems/add-two-numbers/discuss/43105).
+We can just reverse the linked list, and we can use the solution of the [first problem](https://leetcode.com/problems/add-two-numbers/).
+So I do this problem without reversing the linked list.
+
+We need to know the length of each linked list. So we can know when do we start adding the `val`.
+We need to set the answer to a double linked list. Because we might need to modify the upper digits.
+For example 999 + 1.
+
+The time complexity is `O(N)`, `N` is the length of the input linked list.
+The space complexity is `O(N)`, too.
+"""
+class ListNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+        self.prev = None
+
+class Solution(object):
+    def addTwoNumbers(self, A, B):
+        l1 = self.getLength(A)
+        l2 = self.getLength(B)
+        head = ListNode(0)
+        curr = head
+        while A or B:
+            if l1>l2:
+                self.addDigit(curr, A.val)
+                l1-=1
+                A = A.next
+            elif l2>l1:
+                self.addDigit(curr, B.val)
+                l2-=1
+                B = B.next
+            else:
+                val = (A.val if A else 0) + (B.val if B else 0)
+                self.addDigit(curr, val)
+                if l1: l1-=1
+                if l2: l2-=1
+                if A: A = A.next
+                if B: B = B.next
+            curr = curr.next
+        return head if head.val else head.next #remove leading zero
+
+    def getLength(self, L):
+        length = 0
+        while L:
+            length+=1
+            L = L.next
+        return length
+
+    def addDigit(self, node, val):
+        if val<10:
+            node.next = ListNode(val)
+            node.next.prev = node
+        else:
+            node.next = ListNode(val-10)
+            node.next.prev = node
+            node.val+=1
+            while node.val>=10:
+                node.prev.val+=1
+                node.val-=10
+                node = node.prev

problems/add-two-numbers.py

@@ -1,3 +1,4 @@
+#2019/11/17 Update
 """
 Add numbers, units to units digit, tens to tens digit...
 If the added number is greater than 9
@@ -18,7 +19,7 @@ def addTwoNumbers(self, l1, l2):
         while l1 or l2 or temp:
             val = (l1.val if l1 else 0) + (l2.val if l2 else 0) + temp
 
-            if val>9:
+            if val>=10:
                 temp = 1
                 val = val-10
             else:
@@ -32,13 +33,6 @@ def addTwoNumbers(self, l1, l2):
         return pre_head.next
 
 
-
-
-
-
-
-
-
 class Solution(object):
 
     #I like this better and it's faster