diff --git a/18_Hashing/HashSet/prb1.class b/18_Hashing/HashSet/prb1.class
new file mode 100644
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diff --git a/18_Hashing/HashSet/prb1.java b/18_Hashing/HashSet/prb1.java
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+++ b/18_Hashing/HashSet/prb1.java
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+import java.util.*;
+
+public class prb1 {
+    public static void main(String[] args) {
+        int arr[] = {4,3,2,5,6,7,3,4,2,1};
+        HashSet<Integer> set = new HashSet<>();
+
+        for(int i = 0;i<arr.length ;i++){
+            set.add(arr[i]);
+        }
+        System.out.println("ans = " + set.size());
+        //its take 0(n) time complexity..
+    }
+}
diff --git a/18_Hashing/HashSet/tree.class b/18_Hashing/HashSet/tree.class
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diff --git a/18_Hashing/HashSet/tree.java b/18_Hashing/HashSet/tree.java
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+++ b/18_Hashing/HashSet/tree.java
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+import java.util.*;
+
+public class tree {
+    public static void main(String[] args) {
+        TreeSet<String> ts = new TreeSet<>();
+        ts.add("bottle");
+        ts.add("phone");
+        ts.add("sope");
+        ts.add("apple");
+        ts.add("mac");
+
+        for(String obj : ts){
+            System.out.println(obj);
+            //The output is printing in sorted order..
+        }
+        
+
+    }
+}