done

HashSet.java

@@ -0,0 +1,22 @@
+class MyHashSet {
+Set <Integer> s;
+    public MyHashSet() {
+         s=new HashSet<>();
+    }
+
+    public void add(int key) {
+        s.add(key);
+        return ;
+    }
+
+    public void remove(int key) {
+        s.remove(key);
+        return ;
+    }
+
+    public boolean contains(int key) {
+        if(s.contains(key)) return true;
+        return false;
+    }
+}
+

MinStack.java

@@ -0,0 +1,37 @@
+/*used two stack approach , one just noemal and one to store the min val */ 
+
+class MinStack {
+Stack <Integer> st;
+Stack<Integer> mst;
+    public MinStack() {
+        st= new Stack<>();
+        mst= new Stack<>();
+    }
+
+    public void push(int val) {
+        st.push(val);
+        if(mst.isEmpty())
+        {
+            mst.push(val);
+        }
+
+        else
+        {
+            mst.push(Math.min(val, mst.peek()));
+        }
+    }
+
+    public void pop() {
+        st.pop();
+        mst.pop();
+    }
+
+    public int top() {
+        return st.peek();
+    }
+
+    public int getMin() {
+        return mst.peek(); 
+    }
+}
+