diff --git a/Exercise_1.py b/Exercise_1.py
index 532833f5d..1f25ab0ff 100644
--- a/Exercise_1.py
+++ b/Exercise_1.py
@@ -1,21 +1,31 @@
+# Time Complexity: O(1) for push, pop, peek; O(n) for show
+# Space Complexity: O(n) for storing stack elements
+
 class myStack:
-  #Please read sample.java file before starting.
-  #Kindly include Time and Space complexity at top of each file
-     def __init__(self):
-         
-     def isEmpty(self):
-         
-     def push(self, item):
-         
-     def pop(self):
-        
-        
-     def peek(self):
-        
-     def size(self):
-         
-     def show(self):
-         
+    def __init__(self):
+        self.stack = []
+
+    def isEmpty(self):
+        return len(self.stack) == 0
+
+    def push(self, item):
+        self.stack.append(item)
+
+    def pop(self):
+        if not self.isEmpty():
+            return self.stack.pop()
+        return "Stack is empty"
+
+    def peek(self):
+        if not self.isEmpty():
+            return self.stack[-1]
+        return "Stack is empty"
+
+    def size(self):
+        return len(self.stack)
+
+    def show(self):
+        return self.stack
 
 s = myStack()
 s.push('1')
diff --git a/Exercise_2.py b/Exercise_2.py
index b11492215..5a0b10f57 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -6,10 +6,19 @@ def __init__(self, data):
  
 class Stack:
     def __init__(self):
-        
+        self.top = None
+
     def push(self, data):
-        
+        new_node = Node(data)
+        new_node.next = self.top
+        self.top = new_node
+
     def pop(self):
+        if self.top is None:
+            return None
+        popped_data = self.top.data
+        self.top = self.top.next
+        return popped_data
         
 a_stack = Stack()
 while True:
diff --git a/Exercise_3.py b/Exercise_3.py
index a5d466b59..9ff8a20f5 100644
--- a/Exercise_3.py
+++ b/Exercise_3.py
@@ -3,7 +3,9 @@ class ListNode:
     A node in a singly-linked list.
     """
     def __init__(self, data=None, next=None):
-    
+        self.data = data
+        self.next = next
+
 class SinglyLinkedList:
     def __init__(self):
         """
@@ -17,16 +19,41 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
-        
+        new_node = ListNode(data)
+        if not self.head:
+            self.head = new_node
+            return
+        current = self.head
+        while current.next:
+            current = current.next
+        current.next = new_node
+
     def find(self, key):
         """
         Search for the first element with `data` matching
         `key`. Return the element or `None` if not found.
         Takes O(n) time.
         """
-        
+        current = self.head
+        while current:
+            if current.data == key:
+                return current
+            current = current.next
+        return None
+
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        current = self.head
+        previous = None
+        while current:
+            if current.data == key:
+                if previous:
+                    previous.next = current.next
+                else:
+                    self.head = current.next
+                return
+            previous = current
+            current = current.next