diff --git a/DesignHashSet.py b/DesignHashSet.py
new file mode 100644
index 00000000..accdeb0c
--- /dev/null
+++ b/DesignHashSet.py
@@ -0,0 +1,70 @@
+"""
+Approach (double hashing) --
+1. Based on constraints, take the primary array range to be sqrt(10^6)
+2. Use mod hash function to get index of the element in primary array
+3. For add(), if there's no value present at this index, we initiate a Boolean secondary array of size sqrt(10^6)
+4. For the secondary array we use division hash function. why division? -> since if mod is used again, all the elements which were earlier causing collision, will again collide at the same index in secondary array
+
+why secondary array data type is Boolean?
+since size is smaller than storing an int
+
+TC - O(1) for add, remove, contains since constant lookup
+SC - O(n) since using array of size n
+"""
+
+
+class MyHashSet:
+
+    def __init__(self):
+        self.buckets = 1000
+        self.bucketItems = [None] * self.buckets
+
+    # primary array hash function
+    def getBucket(self, key):
+        return key % self.buckets
+
+    # secondary array hash function
+    def getBucketItems(self, key):
+        return key // self.buckets
+
+    def add(self, key: int) -> None:
+        bucket = self.getBucket(key)
+        bucketItem = self.getBucketItems(key)
+
+        # edge case when we need to add at 0th index
+        # if required to add 1000000. 1000000%1000 = 0 and 1000000//1000 = 1000
+        # we have 0 to 999 in the secondary array so for 1000000, we'll get index out of range
+        if not self.bucketItems[bucket] and bucket == 0:
+            self.bucketItems[bucket] = [False] * (self.buckets + 1)
+
+        # initialize secondary array
+        elif not self.bucketItems[bucket]:
+            self.bucketItems[bucket] = [False] * self.buckets
+
+        # add the element
+        self.bucketItems[bucket][bucketItem] = True
+
+    def remove(self, key: int) -> None:
+        bucket = key % self.buckets
+        bucketItem = key // self.buckets
+
+        # if secondary array not present, return False
+        if not self.bucketItems[bucket]: return False
+
+        # remove item by marking it False
+        self.bucketItems[bucket][bucketItem] = False
+
+    def contains(self, key: int) -> bool:
+        bucket = key % self.buckets
+        bucketItem = key // self.buckets
+
+        # if secondary array not present, return False
+        if not self.bucketItems[bucket]: return False
+
+        return self.bucketItems[bucket][bucketItem]
+
+# 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/MinStack.py b/MinStack.py
new file mode 100644
index 00000000..3cc7279b
--- /dev/null
+++ b/MinStack.py
@@ -0,0 +1,52 @@
+"""
+Using 1 stack (deque)
+TC - O(1) for all 4 operations
+SC - O(n)
+"""
+import sys
+from collections import deque
+
+
+class MinStack:
+
+    def __init__(self):
+        self.minstack = deque()
+        self.minVal = sys.maxsize
+        self.minstack.append(self.minVal)
+
+    def push(self, val: int) -> None:
+        if val <= self.minVal:
+            self.minstack.append(self.minVal)
+            self.minVal = val
+        self.minstack.append(val)
+
+    def pop(self) -> None:
+        if len(self.minstack) != 0:
+            if self.minstack.pop() == self.minVal:
+                self.minVal = self.minstack.pop()
+
+    def top(self) -> int:
+        if len(self.minstack) != 0:
+            return self.minstack[-1]
+        return -1
+
+    def getMin(self) -> int:
+        return self.minVal
+
+
+# Your MinStack object will be instantiated and called as such:
+obj = MinStack()
+obj.push(5)
+obj.push(4)
+print("Min val is: ", obj.getMin())
+obj.push(3)
+obj.push(10)
+obj.pop()
+print("Min val is: ", obj.getMin())
+obj.push(0)
+print("Min val is: ", obj.getMin())
+obj.pop()
+obj.pop()
+obj.pop()
+print("Min val is: ", obj.getMin())
+print(obj.top())