From b267714124910b8976d7a4bde644c4aab6561403 Mon Sep 17 00:00:00 2001
From: Shaikh Israil <shaikh.israil@oracle.com>
Date: Sat, 31 Jan 2026 21:12:34 -0800
Subject: [PATCH 1/4] exercise 1

---
 Exercise_1.py | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/Exercise_1.py b/Exercise_1.py
index 532833f5d..28dfe2556 100644
--- a/Exercise_1.py
+++ b/Exercise_1.py
@@ -1,20 +1,34 @@
+#  Time Complexity : Push: O(1), POP: O(1), Peek: O(1), size: O(1)
+
+#  Space Complexity : O(N)
+
 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 __init__(self):
+      self.arr = []
+
+    def isEmpty(self):
+        if len(self.arr) == 0:
+            return True
+        return False
+    
+    def push(self, item):
+        self.arr.append(item)
+        print(self.arr)
+            
+    def pop(self):
+        return self.arr.pop()
+      
+    def peek(self):
+      if self.arr:
+         return self.arr[-1]
+
+    def size(self):
+       return len(self.arr)
         
-     def size(self):
-         
-     def show(self):
+    def show(self):
+       return self.arr
          
 
 s = myStack()

From 92d4b07ad9e36bc379aab1dcd566c976f6458de3 Mon Sep 17 00:00:00 2001
From: Shaikh Israil <shaikh.israil@oracle.com>
Date: Sat, 31 Jan 2026 21:20:27 -0800
Subject: [PATCH 2/4] Excercise 2

---
 Exercise_2.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Exercise_2.py b/Exercise_2.py
index b11492215..81438bba7 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -1,4 +1,6 @@
+#  Time Complexity : push: O(1)
 
+#  Space Complexity : pop: O(1)
 class Node:
     def __init__(self, data):
        self.data = data
@@ -6,10 +8,13 @@ def __init__(self, data):
  
 class Stack:
     def __init__(self):
+        self.arr = []
         
     def push(self, data):
+        self.arr.append(data)
         
     def pop(self):
+        return self.arr.pop()
         
 a_stack = Stack()
 while True:

From 4f64df35982e85936b8744fd1a2dc7046c17a642 Mon Sep 17 00:00:00 2001
From: Shaikh Israil <shaikh.israil@oracle.com>
Date: Sun, 8 Feb 2026 15:36:15 -0800
Subject: [PATCH 3/4] Exercise 3- Linked list impl

---
 Exercise_3.py | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/Exercise_3.py b/Exercise_3.py
index a5d466b59..62d66b0fb 100644
--- a/Exercise_3.py
+++ b/Exercise_3.py
@@ -3,6 +3,7 @@ class ListNode:
     A node in a singly-linked list.
     """
     def __init__(self, data=None, next=None):
+        self.val = data
     
 class SinglyLinkedList:
     def __init__(self):
@@ -10,13 +11,18 @@ def __init__(self):
         Create a new singly-linked list.
         Takes O(1) time.
         """
-        self.head = None
+        self.head = ListNode(-1)
 
     def append(self, data):
         """
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        curr = self.head
+        node = ListNode(data)
+        while curr.next != None:
+            curr = curr.next
+        curr.next = node
         
     def find(self, key):
         """
@@ -24,9 +30,22 @@ def find(self, key):
         `key`. Return the element or `None` if not found.
         Takes O(n) time.
         """
+        curr = self.head.next
+        while curr:
+            if curr.data == key:
+                return curr
+        return None
         
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        curr = self.head.next
+        prev = None
+        while curr and curr.data != key:
+            prev = curr
+            curr = curr.next
+        if prev:
+            prev.next = curr.next
+        return

From 2488b9530a2f342e9fea2d6ddc26fcb37e9f4c5e Mon Sep 17 00:00:00 2001
From: Shaikh Israil <shaikh.israil@oracle.com>
Date: Sun, 8 Feb 2026 16:00:10 -0800
Subject: [PATCH 4/4] implement using linkedlist - Ex 2

---
 Exercise_2.py | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/Exercise_2.py b/Exercise_2.py
index 81438bba7..71ae550b7 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -8,13 +8,18 @@ def __init__(self, data):
  
 class Stack:
     def __init__(self):
-        self.arr = []
+        self.head = Node(-1)
         
     def push(self, data):
-        self.arr.append(data)
+        node = Node(data)
+        node.next = self.head.next
+        self.head.next = node
         
     def pop(self):
-        return self.arr.pop()
+        curr = self.head.next
+        if curr:
+            self.head.next = curr.next
+        return curr.data if curr else None
         
 a_stack = Stack()
 while True: