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/Backtracking-2.iml b/.idea/Backtracking-2.iml
new file mode 100644
index 00000000..b107a2dd
--- /dev/null
+++ b/.idea/Backtracking-2.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..639900d1
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectRootManager">
+    <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..96d9dd7d
--- /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/Backtracking-2.iml" filepath="$PROJECT_DIR$/.idea/Backtracking-2.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/SubSets.java b/SubSets.java
new file mode 100644
index 00000000..14f14efb
--- /dev/null
+++ b/SubSets.java
@@ -0,0 +1,27 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class SubSets {
+    public List<List<Integer>> subsets(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+        List<Integer> currSet = new ArrayList<>();
+        helper(nums, result, currSet, 0);
+        return result;
+    }
+    private void helper(int[] nums, List<List<Integer>> result, List<Integer> currSet, int idx){
+        //base
+        if(idx == nums.length){
+            result.add(new ArrayList<>(currSet));
+            return;
+        }
+        //logic
+        //choose
+        currSet.add(nums[idx]);
+        helper(nums, result, currSet, idx+1);
+        currSet.remove(currSet.size()-1);
+
+        //no choose
+        helper(nums, result, currSet, idx+1);
+
+    }
+}