Done PreCourse-1

Exercise_1.py

@@ -2,19 +2,40 @@ class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+          self.value = []
 
      def isEmpty(self):
+          return len(self.value) == 0
 
      def push(self, item):
+          self.value.append(item)
+
 
      def pop(self):
+          if  not self.isEmpty():
+              return self.value.pop()
+
+          return  "Stake is empty!"
+
 
 
      def peek(self):
+          if not self.isEmpty():
+               return self.value[-1]
+
+          return  "Stake is empty!"
+
+
 
      def size(self):
 
+        return len(self.value)
+
      def show(self):
+          if self.isEmpty():
+               return "Sorry,there is No items in the list"
+          return self.value
+
 
 
 s = myStack()

Exercise_2.py

@@ -6,10 +6,20 @@ 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:

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 = None
 
 class SinglyLinkedList:
     def __init__(self):
@@ -13,20 +15,64 @@ def __init__(self):
         self.head = None
 
     def append(self, data):
+
+        new_node = ListNode(data)
+
+        if self.head is None:
+            self.head = new_node
+            return
+
+        current = self.head
+        if current.next is not None:
+            current = current.next
+
+        current.next = new_node
+
+
         """
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+
 
     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
+
+        if current is None:
+            return None
+
+        if current.data == key:
+            self.head = current.next
+            current = None
+            return
+
+        while current:
+            if current.data == key:
+                previous.next = current.next
+                current = None
+            previous = current
+            current = current.next
+        return None
+