diff --git a/MinStack.java b/MinStack.java
new file mode 100644
index 00000000..82ce0789
--- /dev/null
+++ b/MinStack.java
@@ -0,0 +1,38 @@
+// O(1) time complexity for all operations
+// O(n) space complexity
+
+import java.util.Stack;
+
+class MinStack {
+    Stack<Integer> minStack;
+    int min;
+
+    public MinStack() {
+        minStack = new Stack<>();
+        min = Integer.MAX_VALUE;
+    }
+    
+    public void push(int val) {
+        if (val <= min) {
+            minStack.push(min); // push min
+            min = val;
+        }
+        minStack.push(val); // push val as it tracks curr min
+    }
+    
+    public void pop() {
+        int popped = minStack.pop();
+        if (popped == min) {
+            min = minStack.pop();
+        }
+    }
+    
+    public int top() {
+        return minStack.peek();
+    }
+    
+    public int getMin() {
+        return min;
+    }
+}
+
diff --git a/MyHashSet.java b/MyHashSet.java
new file mode 100644
index 00000000..e1cbd79b
--- /dev/null
+++ b/MyHashSet.java
@@ -0,0 +1,54 @@
+// O(1) time, O(1) space
+
+class MyHashSet {
+
+    boolean[][] storage;
+    int primaryBuckets;
+    int secondaryBuckets;
+
+    public MyHashSet() {
+        primaryBuckets = 1000;
+        secondaryBuckets = 1000;
+        storage = new boolean[primaryBuckets][];
+    }
+    
+    private int getPrimaryHash(int key) {
+        return key % primaryBuckets;
+    }
+
+    private int getSecondaryHash(int key) {
+        return key / secondaryBuckets;
+    }
+
+    public void add(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if (storage[primaryHash] == null) {
+            if (primaryHash == 0) {
+                storage[primaryHash] = new boolean[secondaryBuckets + 1];
+            }
+            else {
+                storage[primaryHash] = new boolean[secondaryBuckets];
+            }
+        }
+        int secondaryHash = getSecondaryHash(key);
+        storage[primaryHash][secondaryHash] = true;
+    }
+    
+    public void remove(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if (storage[primaryHash] == null) {
+            return;
+        }
+        int secondaryHash = getSecondaryHash(key);
+        storage[primaryHash][secondaryHash] = false;
+    }
+    
+    public boolean contains(int key) {
+        int primaryHash = getPrimaryHash(key);
+        if (storage[primaryHash] == null) {
+            return false;
+        }
+        int secondaryHash = getSecondaryHash(key);
+        return storage[primaryHash][secondaryHash];
+    }
+}