no message

Author: Chris Wu

problems/add-two-numbers.py

@@ -1,3 +1,44 @@
+"""
+Add numbers, units to units digit, tens to tens digit...
+If the added number is greater than 9
+We will add 1 to next digit (`temp`) and only take the units digit of the added value.
+
+For example, if we are adding units digits, 3 and 9, the sum is 12.
+12 is greater than the 9, so we set `temp` to 1, so when we are calculating tens digits it will `+1`.
+And we only take the units digit of 12, which is `12 - 10 = 2`.
+
+The time complexity is O(N), N is the length of two linked list.
+Space complexity is O(N), since we need to store a new linked list.
+"""
+class Solution(object):
+    def addTwoNumbers(self, l1, l2):
+        temp = 0
+        pre_head = ListNode(-1)
+        curr = pre_head
+        while l1 or l2 or temp:
+            val = (l1.val if l1 else 0) + (l2.val if l2 else 0) + temp
+
+            if val>9:
+                temp = 1
+                val = val-10
+            else:
+                temp = 0
+
+            curr.next = ListNode(val)
+
+            if l1: l1 = l1.next
+            if l2: l2 = l2.next
+            curr = curr.next
+        return pre_head.next
+
+
+
+
+
+
+
+
+
 class Solution(object):
 
     #I like this better and it's faster
@@ -14,18 +55,18 @@ def getTotal(l):
                 x+=1
                 l = l.next
             return total
-        
+
         total = getTotal(l1)+getTotal(l2)
 
         #put the number back into linked list
         num_string = str(total)[::-1]
         pre = ListNode(None)
         curr = pre
-        
+
         for n in num_string:
             curr.next = ListNode(int(n))
             curr = curr.next
-            
+
         return pre.next
 
 
@@ -45,27 +86,27 @@ def addTwoNumbers(self, l1, l2):
 
         while l1 or l2:
             total = carry
-            
+
             if l1:
                 total+=l1.val
                 l1 = l1.next
             if l2:
                 total+=l2.val
                 l2 = l2.next
-                
+
             if total>=10:
                 carry=1
                 curr.next = ListNode(total%10)
             else:
                 carry = 0
                 curr.next = ListNode(total)
-            
+
             curr = curr.next
-        
+
         #check if there is carry left behind, for example
         #[5]+[5]=[0,1]
         #both linked list are done iterate, but still haven't finish adding
         if carry!=0:
             curr.next = ListNode(carry)
-            
-        return pre.next
+
+        return pre.next