Completed Design-1.

Design HashSet.java

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+//Approach : 
+//TC : O(1)
+//SC : O(1)
+class MyHashSet {
+    int primaryKeyLen = 1000;
+    int secondaryKeyLen = 1000;
+    boolean[][] set;
+
+    public MyHashSet() {
+        set = new boolean[1000][]; //SC: 10^3 = constant
+    }
+
+    public void add(int key) { //TC: O(1) // SC: 10^3= constant = O(1)
+        int z = key % primaryKeyLen;
+        if (set[z] == null) {
+            set[z] = new boolean[1000]; //SC: 10^3 = constant
+        }
+        int s = key / 1000;
+        set[z][s] = true;
+    }
+
+    public void remove(int key) { //TC: O(1), SC: O(1)
+        int z = key % 1000;
+        int s = key / 1000;
+        if (set[z] == null) {
+            return;
+        }
+        set[z][s] = false;
+    }
+
+    public boolean contains(int key) {//TC: O(1), SC:O(1)
+        int z = key % 1000;
+        int s = key / 1000;
+        if (set[z] == null) {
+            return false;
+        }
+        if (set[z][s] == true) {
+            return true;
+        }
+        return false;
+    }
+}
+
+/**
+ * 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);
+ */

minStack.java

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+
+import java.util.*;
+//Approach:
+//TC: O(1)
+//SC: 2*O(N)
+
+class MinStack {
+
+    Stack<Integer> st;
+    Stack<Integer> minSt;
+
+    public MinStack() {
+        st = new Stack();
+        minSt = new Stack();
+        minSt.push(Integer.MAX_VALUE);
+    }
+
+    public void push(int value) {
+
+        if (minSt.peek() >= value) {
+            minSt.push(value);
+
+        }
+        st.push(value);
+    }
+
+    public void pop() {
+
+        if (st.peek().equals(minSt.peek())) {
+            minSt.pop();
+        }
+        st.pop();
+
+    }
+
+    public int top() {
+        return st.peek();
+    }
+
+    public int getMin() {
+        return minSt.peek();
+    }
+}
+
+/**
+ * Your MinStack object will be instantiated and called as such:
+ * MinStack obj = new MinStack();
+ * obj.push(value);
+ * obj.pop();
+ * int param_3 = obj.top();
+ * int param_4 = obj.getMin();
+ */