add: KthSmallestNumberInBSTIterative

Author: Jer3myYu

java/Trees/KthSmallestNumberInBSTIterative.java

@@ -0,0 +1,41 @@
+import java.util.Stack;
+
+import DS.TreeNode;
+
+/*
+    // Definition of TreeNode:
+    class TreeNode {
+        public int val;
+        public TreeNode left;
+        public TreeNode right;
+        public TreeNode(int val) {
+            this.val = val;
+        }
+    }
+ */
+
+public class KthSmallestNumberInBSTIterative {
+    public int kthSmallestNumberInBSTIterative(TreeNode root, int k) {
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode node = root;
+        while (!stack.isEmpty() || node != null) {
+            // Move to the leftmost node and add nodes to the stack as we go so they 
+            // can be processed in future iterations.
+            while (node != null) {
+                stack.push(node);
+                node = node.left;
+            }
+            // Pop the top node from the stack to process it, and decrement 'k'.
+            node = stack.pop();
+            k--;
+            // If we have processed 'k' nodes, return the value of the 'k'th smallest 
+            // node.
+            if (k == 0) {
+                return node.val;
+            }
+            // Move to the right subtree.
+            node = node.right;
+        }
+        return -1;
+    }
+}