update

Author: kamyu104

Python/binary-search-tree-iterator.py

@@ -0,0 +1,35 @@
+# Definition for a  binary tree node
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+class BSTIterator:
+    # @param root, a binary search tree's root node
+    def __init__(self, root):
+        self.stack = []
+        self.cur = root
+
+    # @return a boolean, whether we have a next smallest number
+    def hasNext(self):
+        return self.stack or self.cur
+
+    # @return an integer, the next smallest number
+    def next(self):
+        while self.cur:
+            self.stack.append(self.cur)
+            self.cur = self.cur.left
+        
+        self.cur = self.stack.pop()
+        node = self.cur
+        self.cur = self.cur.right
+        
+        return node.val
+        
+if __name__ == "__main__":
+    root = TreeNode(2)
+    root.left = TreeNode(1)
+    i, v = BSTIterator(root), []
+    while i.hasNext(): v.append(i.next())
+    print v

README.md

@@ -1,9 +1,9 @@
 LeetCode
 ======== 
 
-Up to date (2014-12-30), there are total `172` problems on [LeetCode Online Judge](https://oj.leetcode.com/).
+Up to date (2014-12-31), there are total `173` problems on [LeetCode Online Judge](https://oj.leetcode.com/).
 The number of problems is increasing recently.
-Here is the classification of all `172` problems.
+Here is the classification of all `173` problems.
 I'll keep updating for full summary and better solutions. Stay tuned for updates.
 
 --- 
@@ -204,13 +204,16 @@ Problem         |  Solution       |  Time           | Space           | Difficul
 ##Stack
 Problem         |  Solution       |  Time           | Space           | Difficulty     | Notes
 --------------- | --------------- | --------------- | --------------- | -------------- | -----
+[Binary Search Tree Iterator] | [binary-search-tree-iterator.py] | _O(1)_| _O(logn)_| Medium   
 [Evaluate Reverse Polish Notation]| [evaluate-reverse-polish-notation.py]| _O(n)_| _O(n)_| Medium          |
 [Longest Valid Parentheses]| [longest-valid-parentheses.py] | _O(n)_ | _O(1)_ | Hard   |
 [Min Stack]     | [min-stack.py]  | _O(n)_          | _O(1)_          | Easy           |
 [Simplify Path]| [simplify-path.py] | _O(n)_        | _O(n)_          | Medium         |
 [Symmetric Tree]| [symmetric-tree.py] | _O(n)_      | _O(logn)_       | Easy           |
 [Valid Parentheses]| [valid-parentheses.py] | _O(n)_        | _O(n)_          | Easy           |
 
+[Binary Search Tree Iterator]:https://oj.leetcode.com/problems/binary-search-tree-iterator/
+[binary-search-tree-iterator.py]:https://github.com/kamyu104/LeetCode/blob/master/Python/binary-search-tree-iterator.py
 [Evaluate Reverse Polish Notation]:https://oj.leetcode.com/problems/evaluate-reverse-polish-notation/
 [evaluate-reverse-polish-notation.py]:https://github.com/kamyu104/LeetCode/blob/master/Python/evaluate-reverse-polish-notation.py
 [Longest Valid Parentheses]:https://oj.leetcode.com/problems/longest-valid-parentheses/