diff --git a/problem1.py b/problem1.py
new file mode 100644
index 00000000..7e277b7a
--- /dev/null
+++ b/problem1.py
@@ -0,0 +1,64 @@
+class MyHashSet:
+
+    def __init__(self):
+        self.keyRange = 769
+        self.bucketArray = [Bucket() for i in range(self.keyRange)]
+    
+    def _hash(self,key):
+        return key % self.keyRange
+
+    def add(self, key: int) -> None:
+        bucketIndex = self._hash(key)
+        self.bucketArray[bucketIndex].insert(key)
+
+    def remove(self, key: int) -> None:
+        bucketIndex = self._hash(key)
+        self.bucketArray[bucketIndex].delete(key)
+
+    def contains(self, key: int) -> bool:
+        bucketIndex = self._hash(key)
+        return self.bucketArray[bucketIndex].exists(key)
+
+class Node:
+    def __init__(self, value, nextNode=None):
+        self.value = value
+        self.next = nextNode
+
+class Bucket:
+    def __init__(self):
+        # a pseudo head
+        self.head = Node(0)
+
+    def insert(self, newValue):
+        # if not existed, add the new element to the head.
+        if not self.exists(newValue):
+            newNode = Node(newValue, self.head.next)
+            # set the new head.
+            self.head.next = newNode
+
+    def delete(self, value):
+        prev = self.head
+        curr = self.head.next
+        while curr is not None:
+            if curr.value == value:
+                # remove the current node
+                prev.next = curr.next
+                return
+            prev = curr
+            curr = curr.next
+
+    def exists(self, value):
+        curr = self.head.next
+        while curr is not None:
+            if curr.value == value:
+                # value existed already, do nothing
+                return True
+            curr = curr.next
+        return False
+
+
+# Your MyHashSet object will be instantiated and called as such:
+# obj = MyHashSet()
+# obj.add(key)
+# obj.remove(key)
+# param_3 = obj.contains(key)
\ No newline at end of file
diff --git a/problem2.py b/problem2.py
new file mode 100644
index 00000000..1c17748e
--- /dev/null
+++ b/problem2.py
@@ -0,0 +1,36 @@
+# time: O(n)
+# space: O(n)
+
+class MinStack:
+
+    def __init__(self):
+        self.stack = []
+        self.minStack = []
+
+    def push(self, val: int) -> None:
+        self.stack.append(val)
+        if self.minStack and val <= self.minStack[-1]:
+            self.minStack.append(val)
+        elif len(self.minStack)==0:
+            self.minStack.append(val)
+
+    def pop(self) -> None:
+        if self.stack[-1] == self.minStack[-1]:
+            self.minStack.pop()
+        self.stack.pop()
+        
+
+    def top(self) -> int:
+        return self.stack[-1]
+
+    def getMin(self) -> int:
+        return self.minStack[-1]
+        
+
+
+# Your MinStack object will be instantiated and called as such:
+# obj = MinStack()
+# obj.push(val)
+# obj.pop()
+# param_3 = obj.top()
+# param_4 = obj.getMin()
\ No newline at end of file