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-# Algorithms 2019-2020 Python LEETCODE
-
-Check branches for information.
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+# Binary tree
+
++ [Binary Search Tree Iterator](#binary-search-tree-iterator)
+
+## Binary Search Tree Iterator
+
+https://leetcode.com/problems/binary-search-tree-iterator/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class BSTIterator(object):
+
+    def traverse(self, node):
+        """
+        :type node: TreeNode
+        """
+        while node:
+            self.inorderlist.append(node)
+            node = node.left
+
+    def __init__(self, root):
+        """
+        :type root: TreeNode
+        """
+        self.root = root
+        self.inorderlist = []
+        self.traverse(root)
+
+    def next(self):
+        """
+        @return the next smallest number
+        :rtype: int
+        """
+        node = self.inorderlist.pop()
+        self.traverse(node.right)
+        return node.val
+
+    def hasNext(self):
+        """
+        @return whether we have a next smallest number
+        :rtype: bool
+        """
+        return len(self.inorderlist) != 0
+
+# Your BSTIterator object will be instantiated and called as such:
+# obj = BSTIterator(root)
+# param_1 = obj.next()
+# param_2 = obj.hasNext()
+
+```
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