add a solution (#30)

Author: sangheestyle

Python/kth-smallest-element-in-a-bst.py

@@ -21,3 +21,28 @@ def kthSmallest(self, root, k):
 
         return float("-inf")
 
+
+# time: O(max(h, k))
+# space: O(h)
+
+from itertools import islice
+
+
+class Solution2(object):
+    def kthSmallest(self, root, k):
+        """
+        :type root: TreeNode
+        :type k: int
+        :rtype: int
+        """
+        def gen_inorder(root):
+            if root:
+                for n in gen_inorder(root.left):
+                    yield n
+
+                yield root.val
+
+                for n in gen_inorder(root.right):
+                    yield n
+
+        return next(islice(gen_inorder(root), k-1, k))