From d159dae194cddd93629ceaf891ac7770c391b98d Mon Sep 17 00:00:00 2001
From: Melvin Milkiyas <melvinmilkiyas98@gmail.com>
Date: Tue, 11 Nov 2025 23:07:42 -0800
Subject: [PATCH] Precourse 1 - completed

---
 Exercise_1.py | 60 ++++++++++++++++++++++++++++++++++++++++++++++++---
 Exercise_2.py | 18 +++++++++++++++-
 Exercise_3.py | 34 +++++++++++++++++++++++++++++
 3 files changed, 108 insertions(+), 4 deletions(-)

diff --git a/Exercise_1.py b/Exercise_1.py
index 532833f5d..609e07718 100644
--- a/Exercise_1.py
+++ b/Exercise_1.py
@@ -1,24 +1,78 @@
+
+### Stack with array
+
+
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+         self.stack = []
+         self.MAX = 5
+
+         
+     def size(self):
+         return len(self.stack)
+         #Time complexity O(1)
+    
          
      def isEmpty(self):
+         if self.size()==0:
+             return True
+         else:
+            return False
+          #Time complexity O(1)
+    
          
      def push(self, item):
+         if self.size()!=self.MAX:
+             self.stack.append(item)
+         else:
+             print("Stack is full")
+         return self.stack
+         #Time complexity O(1)
+
          
      def pop(self):
+         if not self.isEmpty():
+             p=self.stack.pop()
+             return p
+         else:
+             print("Stack is empty")
+             return None
+          #Time complexity O(1)
+
         
         
      def peek(self):
-        
-     def size(self):
+         if not self.isEmpty():
+             return self.stack[-1]
+         else:
+             return None
+          #Time complexity O(1)
+    
          
      def show(self):
-         
+         return self.stack
+         #Time complexity O(1)
+# Space Complexity: O(n)     
 
 s = myStack()
 s.push('1')
 s.push('2')
+s.push('3')
+s.push('4')
+s.push('5')
+s.push('6')
+
+
+print(s.pop())
+print(s.pop())
+print(s.pop())
 print(s.pop())
+
+
+
 print(s.show())
+print(s.peek())
+
+
diff --git a/Exercise_2.py b/Exercise_2.py
index b11492215..5100245c4 100644
--- a/Exercise_2.py
+++ b/Exercise_2.py
@@ -6,10 +6,26 @@ def __init__(self, data):
  
 class Stack:
     def __init__(self):
+        self.top = None
+        self.count = 0
         
     def push(self, data):
-        
+        new_node = Node(data)
+        new_node.next = self.top
+        self.top = new_node
+        self.count+=1
+         #Time complexity O(1)
+                
     def pop(self):
+        if self.top == None:
+            return None
+        else:
+            p = self.top.data
+            self.top = self.top.next
+            self.count -=1
+            return p
+         #Time complexity O(1)
+  #Space complexity O(n)                   
         
 a_stack = Stack()
 while True:
diff --git a/Exercise_3.py b/Exercise_3.py
index a5d466b59..2de832772 100644
--- a/Exercise_3.py
+++ b/Exercise_3.py
@@ -3,6 +3,8 @@ 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):
@@ -11,22 +13,54 @@ def __init__(self):
         Takes O(1) time.
         """
         self.head = None
+        
 
     def append(self, data):
         """
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        new_node = ListNode(data)
+        if self.head == None:
+            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.data
+            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_node = None
+     
+        while current:
+            if current.data == key:
+                if previous_node:
+                    previous_node.next=current.next
+                    return
+                else:
+                    self.head = current.next
+            previous_node = current
+            current=current.next