Update strobogrammatic-number-ii.py

Author: kamyu104

Python/strobogrammatic-number-ii.py

@@ -2,24 +2,38 @@
 # Space: O(n)
 
 class Solution(object):
-    lookup = {'0':'0', '1':'1', '6':'9', '8':'8', '9':'6'}
-
-    # @param {integer} n
-    # @return {string[]}
     def findStrobogrammatic(self, n):
-        return self.findStrobogrammaticRecu(n, n)
+        """
+        :type n: int
+        :rtype: List[str]
+        """
+        lookup = {'0':'0', '1':'1', '6':'9', '8':'8', '9':'6'}
+        result = ['0', '1', '8'] if n%2 else ['']
+        for i in xrange(n%2, n, 2):
+            result = [a + num + b for a, b in lookup.iteritems() if i != n-2 or a != '0' for num in result]
+        return result
 
-    def findStrobogrammaticRecu(self, n, k):
-        if k == 0:
-            return ['']
-        elif k == 1:
-            return ['0', '1', '8']
 
-        result = []
-        for num in self.findStrobogrammaticRecu(n, k - 2):
-            for key, val in self.lookup.iteritems():
-                if n != k or key != '0':
-                    result.append(key + num + val)
+# Time:  O(n * 5^(n/2))
+# Space: O(n)
+class Solution2(object):
+    def findStrobogrammatic(self, n):
+        """
+        :type n: int
+        :rtype: List[str]
+        """
+        lookup = {'0':'0', '1':'1', '6':'9', '8':'8', '9':'6'}
+        def findStrobogrammaticRecu(n, k):
+            if k == 0:
+                return ['']
+            elif k == 1:
+                return ['0', '1', '8']
+            result = []
+            for num in findStrobogrammaticRecu(n, k - 2):
+                for key, val in lookup.iteritems():
+                    if n != k or key != '0':
+                        result.append(key + num + val)
+            return result
 
-        return result
+        return findStrobogrammaticRecu(n, n)