diff --git a/QueueUsingStack.py b/QueueUsingStack.py
new file mode 100644
index 00000000..2a4be865
--- /dev/null
+++ b/QueueUsingStack.py
@@ -0,0 +1,46 @@
+# used 2 stacks to implement queue.
+# before performing pop and peek check move all the items to outstack if that is empty.
+# time complexity for push and isempty - O(1)
+# time complexity for pop and peek - O(N)
+class MyQueue:
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.inStack = [] # initializing python list as instack
+        self.outStack = [] # initializing python list as outstack
+
+    def push(self, x: int) -> None:
+        """
+        Push element x to the back of queue.
+        """
+
+        self.inStack.append(x) # push new items to instack
+        # print(self.inStack, self.outStack)
+
+    def pop(self) -> int:
+        """
+        Removes the element from in front of queue and returns that element.
+        """
+        self.moveItems() # calling move method.
+        return self.outStack.pop() # pop peek(top) item from outstack
+
+    def peek(self) -> int:
+        """
+        Get the front element.
+        """
+        self.moveItems() # calling move method.
+        return self.outStack[-1] # extracting top element i.e., last inserted item to the outstack.
+
+    def empty(self) -> bool:
+        """
+        Returns whether the queue is empty.
+        """
+        if not self.inStack and not self.outStack:
+            return True # if both stacks are empty return true.
+
+    def moveItems(self):
+        if not self.outStack: # if outstack is empty then push all items from instack to outstack
+            while self.inStack:
+                self.outStack.append(self.inStack.pop()) # pop one item at a time from instack and push to outstack.
\ No newline at end of file
diff --git a/hashset_4(usingDoubleHash).py b/hashset_4(usingDoubleHash).py
new file mode 100644
index 00000000..1cf96e13
--- /dev/null
+++ b/hashset_4(usingDoubleHash).py
@@ -0,0 +1,49 @@
+# As per the class I tried double hashing technique for hashset, in leetcode failed 4 testcases. Not sure.
+# My challenges were Initializing lists with boolean variables, and accessing public variables where i was stuck.
+class MyHashSet:
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.buckets = 1000 # list of 1000 items
+        self.bucketItems = 1000 # list of 1000 items
+        self.storage = [None for i in range(self.buckets)] # initializing list variables as None at beginning
+
+    def bucketsHash(self, value):
+        return value % self.buckets #return hash code
+
+    def bucketItemsHash(self, value):
+        return value % self.bucketItems # return hashcode
+
+    def add(self, value: int) -> None:
+        buc = self.bucketsHash(value) # get the hashcode for main list
+        bucItem = self.bucketItemsHash(value) # get the hash code for sublist
+        # print(buc,bucItem)
+        if self.storage[buc] is None:
+            self.storage[buc] = [None for i in range(self.bucketItems)] # if main list is none initialize sublist
+        if self.storage[buc] is not None and self.storage[buc][bucItem] is None:
+            # if main list is initialized and having a sublist and sublist hash item
+            # is None then initialize it to True which adds an item.
+            self.storage[buc][bucItem] = True
+        # print(self.storage[buc][bucItem])
+
+    def remove(self, value: int) -> None:
+        buc = self.bucketsHash(value) # get the hashcode for main list
+        bucItem = self.bucketItemsHash(value) # get the hash code for sublist
+        if self.storage[buc] is not None:
+            # if mainlist is not none then make the item false
+            # to remove the item.
+            self.storage[buc][bucItem] = False
+
+    def contains(self, value: int) -> bool:
+        """
+        Returns true if this set contains the specified element
+        """
+        buc = self.bucketsHash(value) # get the hashcode for main list
+        bucItem = self.bucketItemsHash(value) # get the hash code for sublist
+        if self.storage[buc] is not None and self.storage[buc][bucItem]:
+            # if main list is not none and sublist is true then return true as element is found
+            # else return false as the element doesnt exist.
+            return True
+
diff --git a/hashset_4(usingSingleList).py b/hashset_4(usingSingleList).py
new file mode 100644
index 00000000..5f203272
--- /dev/null
+++ b/hashset_4(usingSingleList).py
@@ -0,0 +1,33 @@
+# time complexity for operations is O(1) but the space required is too high.
+
+class MyHashSet:
+
+    def __init__(self):
+        """
+        Initialize your data structure here.
+        """
+        self.buckets = 1000000 # initializing 1 million records array
+        self.storage = [None for i in range(self.buckets)] #initializing a list
+
+    def bucketsHash(self, value):
+        return value % self.buckets # developing a hash function
+
+    def add(self, value: int) -> None:
+        buc = self.bucketsHash(value) # getting hash value
+        # print(buc,bucItem)
+        # if self.storage[buc] is None:
+        self.storage[buc] = True # inserting true for the data if exists
+        # print(self.storage[buc][bucItem])
+
+    def remove(self, value: int) -> None:
+        buc = self.bucketsHash(value) # getting hash value
+        if self.storage[buc] is not None:
+            self.storage[buc] = False # if the value is present remove it by making false
+
+    def contains(self, value: int) -> bool:
+        """
+        Returns true if this set contains the specified element
+        """
+        buc = self.bucketsHash(value) # getting hash value
+        if self.storage[buc] == True:
+            return True # if the value is present return true.