diff --git a/.idea/.gitignore b/.idea/.gitignore
new file mode 100644
index 00000000..26d33521
--- /dev/null
+++ b/.idea/.gitignore
@@ -0,0 +1,3 @@
+# Default ignored files
+/shelf/
+/workspace.xml
diff --git a/.idea/Trees-1.iml b/.idea/Trees-1.iml
new file mode 100644
index 00000000..b107a2dd
--- /dev/null
+++ b/.idea/Trees-1.iml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
new file mode 100644
index 00000000..919ce1f1
--- /dev/null
+++ b/.idea/codeStyles/Project.xml
@@ -0,0 +1,7 @@
+<component name="ProjectCodeStyleConfiguration">
+  <code_scheme name="Project" version="173">
+    <ScalaCodeStyleSettings>
+      <option name="MULTILINE_STRING_CLOSING_QUOTES_ON_NEW_LINE" value="true" />
+    </ScalaCodeStyleSettings>
+  </code_scheme>
+</component>
\ No newline at end of file
diff --git a/.idea/codeStyles/codeStyleConfig.xml b/.idea/codeStyles/codeStyleConfig.xml
new file mode 100644
index 00000000..a55e7a17
--- /dev/null
+++ b/.idea/codeStyles/codeStyleConfig.xml
@@ -0,0 +1,5 @@
+<component name="ProjectCodeStyleConfiguration">
+  <state>
+    <option name="PREFERRED_PROJECT_CODE_STYLE" value="Default" />
+  </state>
+</component>
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 00000000..f5bd2dfe
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectRootManager" version="2" project-jdk-name="openjdk-25" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/modules.xml b/.idea/modules.xml
new file mode 100644
index 00000000..5cffe90c
--- /dev/null
+++ b/.idea/modules.xml
@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/Trees-1.iml" filepath="$PROJECT_DIR$/.idea/Trees-1.iml" />
+    </modules>
+  </component>
+</project>
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 00000000..35eb1ddf
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/IsValidBST.java b/IsValidBST.java
new file mode 100644
index 00000000..fda722c4
--- /dev/null
+++ b/IsValidBST.java
@@ -0,0 +1,34 @@
+import javax.swing.tree.TreeNode;
+import java.util.LinkedList;
+import java.util.List;
+
+public class IsValidBST {
+    public boolean isValidBST(TreeNode root) {
+        List<Integer> inOrderList = new LinkedList<>();
+        //populate the list
+        helper(root, inOrderList);
+        boolean isBST=true;
+        int prev = inOrderList.get(0);
+        for(int i = 1; i < inOrderList.size(); i++){
+            //check if element is smaller than previous element or if element is duplicate
+            if(inOrderList.get(i)<= prev){
+                isBST = false;
+            }
+            //updating prev element  
+            prev = inOrderList.get(i);
+        }
+        return isBST;
+    }
+
+    void helper(TreeNode treeNode, List<Integer> inOrderList){
+        if(treeNode==null){
+            return;
+        }
+        helper(treeNode.left, inOrderList);
+        inOrderList.add(treeNode.val);
+        helper(treeNode.right, inOrderList);
+    }
+}
+
+//TC: O(N)
+//SC: O(N)