diff --git a/MinStack.java b/MinStack.java
new file mode 100644
index 00000000..247afc4f
--- /dev/null
+++ b/MinStack.java
@@ -0,0 +1,71 @@
+import java.util.Stack;
+
+/*
+Problem 2:
+Design MinStack (https://leetcode.com/problems/min-stack/)
+ */
+public class MinStack {
+    Stack<Integer> st;
+    Stack<Integer> minSt;
+    int min;
+    public MinStack() {
+        this.st = new Stack<>();
+        this.minSt = new Stack<>();
+        this.min = Integer.MAX_VALUE;
+        minSt.push(min);
+    }
+
+    public void push(int val) {
+        min = Math.min(val,min);
+        st.push(val);
+        minSt.push(min);
+    }
+
+    public void pop() {
+        st.pop();
+        minSt.pop();
+        min = minSt.peek();
+    }
+
+    public int top() {
+        return st.peek();
+    }
+
+    public int getMin() {
+        return minSt.peek();
+    }
+}
+
+ class MinStack2 {
+     Stack<Integer> st;
+     int min;
+     public MinStack2() {
+         this.st = new Stack<>();
+
+         this.min = Integer.MAX_VALUE;
+
+     }
+
+     public void push(int val) {
+         if(min>=val){
+             st.push(min);
+         }
+         min = Math.min(val,min);
+         st.push(val);
+     }
+
+     public void pop() {
+         if(st.pop() == min ){
+             min = st.pop();
+         }
+
+     }
+
+     public int top() {
+         return st.peek();
+     }
+
+     public int getMin() {
+         return min;
+     }
+}
diff --git a/MyHashSet.java b/MyHashSet.java
new file mode 100644
index 00000000..78d636aa
--- /dev/null
+++ b/MyHashSet.java
@@ -0,0 +1,55 @@
+//https://leetcode.com/problems/design-hashset/
+public class MyHashSet {
+    int primarySize ;
+    int secondarySize;
+    boolean[][] data;
+
+    public MyHashSet() {
+        this.primarySize = 1001;
+        this.secondarySize = 1000;
+        this.data = new boolean[primarySize][];
+    }
+
+    public void add(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if(this.data[primaryHash]==null){
+            this.data[primaryHash] = new boolean [secondarySize];
+        }
+        int secondaryHash = getSecondaryHash(key);
+        this.data[primaryHash][secondaryHash] = true;
+    }
+
+    public void remove(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if(this.data[primaryHash]==null){
+            return ;
+        }
+        int secondaryHash = getSecondaryHash(key);
+        this.data[primaryHash][secondaryHash] = false;
+    }
+
+    public boolean contains(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if(this.data[primaryHash]==null){
+            return false;
+        }
+        int secondaryHash = getSecondaryHash(key);
+        return  this.data[primaryHash][secondaryHash];
+
+    }
+
+    public int getPrimaryHash(int key){
+        return key/this.primarySize;
+    }
+    public int getSecondaryHash(int key){
+        return key%this.secondarySize;
+    }
+}
+
+/**
+ * Your MyHashSet object will be instantiated and called as such:
+ * MyHashSet obj = new MyHashSet();
+ * obj.add(key);
+ * obj.remove(key);
+ * boolean param_3 = obj.contains(key);
+ */
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