diff --git a/design_hashset.py b/design_hashset.py
new file mode 100644
index 00000000..39f2d71e
--- /dev/null
+++ b/design_hashset.py
@@ -0,0 +1,51 @@
+class MyHashSet:
+    class Node:
+        def __init__(self, key):
+            self.key = key
+            self.next = None
+
+    def __init__(self):
+        self.buckets = 1000
+        self.storage = [None] * self.buckets
+
+    def getHash(self, key):
+        return key % self.buckets
+
+    def getPrev(self, head, key):
+        prev = None
+        curr = head
+        while curr != None and curr.key != key:
+            prev = curr
+            curr = curr.next
+        return prev
+
+    def add(self, key):
+        index = self.getHash(key)
+        if self.storage[index] == None:
+            self.storage[index] = self.Node(-1)
+            self.storage[index].next = self.Node(key)
+            return
+
+        prev = self.getPrev(self.storage[index], key)
+        if prev.next == None:
+            prev.next = self.Node(key)
+
+    def remove(self, key):
+        index = self.getHash(key)
+        if self.storage[index] == None:
+            return
+        prev = self.getPrev(self.storage[index], key)
+        if prev.next == None:
+            return
+        curr = prev.next
+        prev.next = curr.next
+        curr.next = None
+
+    def contains(self, key):
+        index = self.getHash(key)
+        if self.storage[index] == None:
+            return False
+        prev = self.getPrev(self.storage[index], key)
+        if prev.next == None:
+            return False
+        return True
\ No newline at end of file
diff --git a/design_min_stack.py b/design_min_stack.py
new file mode 100644
index 00000000..a2169860
--- /dev/null
+++ b/design_min_stack.py
@@ -0,0 +1,20 @@
+class MinStack:
+    def __init__(self):
+        self.st = []
+        self.min = float('inf')
+
+    def push(self, val: int) -> None:
+        if val <= self.min:
+            self.st.append(self.min)
+            self.min = val
+        self.st.append(val)
+
+    def pop(self) -> None:
+        if self.st.pop() == self.min:
+            self.min = self.st.pop()
+
+    def top(self) -> int:
+        return self.st[-1]
+
+    def getMin(self) -> int:
+        return self.min
\ No newline at end of file