PreCourse 1 Completed

Exercise_1.py

@@ -1,24 +1,52 @@
+# Time Complexity : O(1)
+# Space Complexity : O(1) 
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : No
+
+
+# Your code here along with comments explaining your approach
+
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+         self.arr = list()
 
      def isEmpty(self):
-
+         return self.size() == 0 
+
      def push(self, item):
+         self.arr.append(item)
 
      def pop(self):
-
+         if self.isEmpty():
+             return "Stack is Empty"
+
+         return self.arr.pop()        
 
      def peek(self):
-
-     def size(self):
+         if self.isEmpty():
+             return "Stack is Empty"
+
+         return self.arr[-1]
 
+     def size(self):
+         return len(self.arr)
+
      def show(self):
+         return self.arr
 
 
 s = myStack()
+print("Push: 1")
 s.push('1')
+print("Push: 2")
 s.push('2')
-print(s.pop())
-print(s.show())
+print("Show: ",s.show())
+print("isEmpty: ",s.isEmpty())
+print("Pop: ",s.pop())
+print("Show: ",s.show())
+print("Pop: ",s.pop())
+print("Show: ",s.show())
+print("isEmpty: ",s.isEmpty())
+print("Pop: ",s.pop())

Exercise_2.py

@@ -1,3 +1,10 @@
+# Time Complexity : O(1) with show() it will be O(n)
+# push: O(1)
+# pop: O(1)
+# show: O(n)
+# Space Complexity : O(1)
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : No
 
 class Node:
     def __init__(self, data):
@@ -6,17 +13,43 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.head = None
 
     def push(self, data):
+        newNode = Node(data)
+        current = self.head
+        self.head = newNode
+        self.head.next = current
 
     def pop(self):
+        if self.head is None:
+            return None    
+
+        tmp = self.head.data
+        self.head = self.head.next
+        return tmp
+
+    def show(self):
+        current = self.head
+        if current is None:
+            print("Stack is empty")
+            return
+        print("\n--- Stack (top to bottom) ---")
+        while current is not None:
+            addr = id(current)
+            next_addr = id(current.next) if current.next else None
+            print(f"Data: {current.data} | Address: {addr} | Next: {next_addr}")
+            current = current.next
+        print("-----------------------------\n")
+
 
 a_stack = Stack()
 while True:
     #Give input as string if getting an EOF error. Give input like "push 10" or "pop"
     print('push <value>')
     print('pop')
     print('quit')
+    print('show')
     do = input('What would you like to do? ').split()
     #Give input as string if getting an EOF error. Give input like "push 10" or "pop"
     operation = do[0].strip().lower()
@@ -28,5 +61,7 @@ def pop(self):
             print('Stack is empty.')
         else:
             print('Popped value: ', int(popped))
+    elif operation == 'show':
+        a_stack.show()
     elif operation == 'quit':
         break

Exercise_3.py

@@ -1,8 +1,18 @@
+# Time Complexity : O(n)
+# append: O(n)
+# find: O(n)
+# remove: O(n)
+# Space Complexity : O(1)
+# Did this code successfully run on Leetcode : yes
+# Any problem you faced while coding this : No
+
 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 +21,62 @@ 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.
         """
 
+        if self.head is not None:
+            current = self.head
+            while current.next is not None:    
+                current = current.next
+
+            current.next = ListNode(data)
+        else:    
+            self.head = ListNode(data)
+
     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.
         """
+        if self.head is not None:
+            current = self.head
+            while current is not None:
+                if current.data == key:
+                    return "Found the matching key"
+                current = current.next
+            return None
+        return None
 
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        if self.head is not None:
+            current = self.head
+            pointer = self.head
+            while current is not None:
+                if current.data == key:
+                    if current == self.head:
+                        self.head = self.head.next
+                        return "key removed"
+                    pointer.next = current.next
+                    return "key removed"
+                pointer = current
+                current = current.next
+
+            return None
+        return None
+
+
+
+
+
+
+