solves bst iterator in java

Author: anishLearnsToCode

README.md

@@ -152,7 +152,7 @@
 | 170  | 🔒 [Two Sum  III - Data Structure Design](https://leetcode.com/problems/two-sum-iii-data-structure-design)                                                |                                                                                                                                                                                      |                                                                                                                                   |
 | 171  | [Excel Sheet Column Number](https://leetcode.com/problems/excel-sheet-column-number)                                                                      |                           [![Java](assets/java.png)](src/ExcelSheetColumnNumber.java) [![Python](assets/python.png)](python/excel_sheet_column_number.py)                            |                                                                                                                                   |
 | 172  | [Factoring Trailing Zeroes](https://leetcode.com/problems/factorial-trailing-zeroes)                                                                      |                           [![Java](assets/java.png)](src/FactorialTrailingZeros.java) [![Python](assets/python.png)](python/factorial_trailing_zeroes.py)                            |                                                                                                                                   |
-| 173  | [Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator)                                                                  |                                                                                                                                                                                      |                                                                                                                                   |
+| 173  | [Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator)                                                                  |                                                            [![Java](assets/java.png)](src/BinarySearchTreeIterator.java)                                                             |                                                                                                                                   |
 | 179  | [Largest Number](https://leetcode.com/problems/largest-number)                                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 187  | [Repeated DNA Sequences](https://leetcode.com/problems/repeated-dna-sequences)                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 189  | [Rotate Array](https://leetcode.com/problems/rotate-array)                                                                                                |                                       [![Java](assets/java.png)](src/RotateArray.java) [![Python](assets/python.png)](python/rotate_array.py)                                        |                                                                                                                                   |

src/BinarySearchTreeIterator.java

@@ -0,0 +1,34 @@
+// https://leetcode.com/problems/binary-search-tree-iterator
+// T: O(N)
+// T(next): O(1)
+// T(hasNext): O(1)
+// S: O(log(N))
+
+import java.util.Stack;
+
+public class BinarySearchTreeIterator {
+
+    public static final class BSTIterator {
+        private final Stack<TreeNode> stack = new Stack<>();
+
+        public BSTIterator(TreeNode root) {
+            addLeftNodesPathToStack(root);
+        }
+
+        public int next() {
+            final TreeNode node = stack.pop();
+            addLeftNodesPathToStack(node.right);
+            return node.val;
+        }
+
+        public boolean hasNext() {
+            return !stack.isEmpty();
+        }
+
+        private void addLeftNodesPathToStack(TreeNode root) {
+            if (root == null) return;
+            stack.push(root);
+            addLeftNodesPathToStack(root.left);
+        }
+    }
+}

src/HelloWorld.java

@@ -1,5 +1,16 @@
 public class HelloWorld {
     public static void main(String[] args) {
-        System.out.println(CompareVersionNumbers.compareVersion("0.1", "1.1"));
+        TreeNode root = new TreeNode(7);
+        root.left = new TreeNode(3);
+        root.right = new TreeNode(15);
+        root.right.left = new TreeNode(9);
+        root.right.right = new TreeNode(20);
+
+        TreePrinter.print(root);
+
+        BinarySearchTreeIterator.BSTIterator iterator = new BinarySearchTreeIterator.BSTIterator(root);
+        while (iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
     }
 }