173. Binary Search Tree Iterator

Author: Partho Biswas

README.md

@@ -251,6 +251,7 @@ I have solved quite a number of problems from several topics. See the below tabl
 |06| [739. Daily Temperatures](https://tinyurl.com/ybbezzmt)| [Python](https://tinyurl.com/wu6rdaw/739_Daily_Temperatures.py)| **[Video 1](https://tinyurl.com/sdbkh3z)**, **[Video 2](https://tinyurl.com/rbvaozl)**, [Art 1](https://tinyurl.com/ss3d9tx) | Medium | 📌 TODO: Check again. A tricky one |
 |07| **[150. Evaluate Reverse Polish Notation](https://tinyurl.com/y2xrje8v)** | [Python](https://tinyurl.com/wu6rdaw/150_Evaluate_Reverse_Polish_Notation.py), [Swift](https://tinyurl.com/wuja3c4/150_Evaluate_Reverse_Polish_Notation.swift)| [Vid 1](https://tinyurl.com/s92fp4r) | Medium | --- |
 |08| **[341. Flatten Nested List Iterator](https://tinyurl.com/y6saxwjz)** | [Python](https://tinyurl.com/wu6rdaw/341_Flatten_Nested_List_Iterator.py), [Swift](https://tinyurl.com/wuja3c4/341_Flatten_Nested_List_Iterator.swift)| [Vid 1](https://tinyurl.com/vkj4qll), [Art 1](https://tinyurl.com/wnvvafx), [Art 2](https://tinyurl.com/wmrlxmz), [Art 3](https://tinyurl.com/uplntb3), **[Art 4](https://tinyurl.com/v3q9qfw)**, **[Art 5](https://tinyurl.com/rotxca8)** | Medium | TODO: Check again. Very Important. Learned new things |
+|09| **[173. Binary Search Tree Iterator](https://tinyurl.com/wp2o8h2)** | [Python](https://tinyurl.com/wu6rdaw/173_Binary_Search_Tree_Iterator.py), [Swift](https://tinyurl.com/wuja3c4/173_Binary_Search_Tree_Iterator.swift)| [Vid 1](https://tinyurl.com/vb62v3q), **[Art 1](https://tinyurl.com/smu9ku3)** | Medium | TODO: Check again. Very Important. Learned new things |
 
 </p>
 </details>

leetcode.com/python/173_Binary_Search_Tree_Iterator.py

@@ -0,0 +1,76 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+# Approach 1: https://tinyurl.com/smu9ku3
+class BSTIterator(object):
+
+    def __init__(self, root):
+        """
+        :type root: TreeNode
+        """
+        self.nodesSorted = []
+        self.nextIndex = 0
+        self.__inorder(root)
+
+    def __inorder(self, root):
+        if not root:
+            return
+        self.__inorder(root.left)
+        self.nodesSorted.append(root.val)
+        self.__inorder(root.right)
+
+    def next(self):
+        """
+        @return the next smallest number
+        :rtype: int
+        """
+        value = self.nodesSorted[self.nextIndex]
+        self.nextIndex += 1
+        return value
+
+    def hasNext(self):
+        """
+        @return whether we have a next smallest number
+        :rtype: bool
+        """
+        return self.nextIndex < len(self.nodesSorted)
+
+
+
+
+
+# Approach 2: https://tinyurl.com/smu9ku3
+class BSTIterator(object):
+
+    def __init__(self, root):
+        """
+        :type root: TreeNode
+        """
+        self.stack = []
+        self.__leftMostInorder(root)
+
+    def __leftMostInorder(self, root):
+        while root:
+            self.stack.append(root)
+            root = root.left
+
+    def next(self):
+        """
+        @return the next smallest number
+        :rtype: int
+        """
+        topMostNode = self.stack.pop()
+        if topMostNode.right:
+            self.__leftMostInorder(topMostNode.right)
+        return topMostNode.val
+
+    def hasNext(self):
+        """
+        @return whether we have a next smallest number
+        :rtype: bool
+        """
+        return len(self.stack) > 0

leetcode.com/swift/DS_ALGO_PRAC.playground/Sources/swift/173_Binary_Search_Tree_Iterator.swift

@@ -0,0 +1,2 @@
+import Foundation
+