Pre course 1

Exercise_1.py

@@ -2,19 +2,30 @@ 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 = []
 
      def isEmpty(self):
+       return len(self.stack) == 0
 
      def push(self, item):
+       self.stack.append(item)
 
      def pop(self):
-
+       if self.isEmpty():
+          return "Stack is Empty"
+
+       return self.stack.pop()
 
      def peek(self):
+        if self.isEmpty():
+          return "Stack is Empty"
+        return self.stack[-1]
 
      def size(self):
-
+
+         return len(self.stack)
      def show(self):
+          return self.stack
 
 
 s = myStack()

Exercise_2.py

@@ -6,10 +6,25 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.head = None
 
     def push(self, data):
+        if self.head == None:
+            self.head = Node(data)
+        else:
+            nw = Node(data)
+            nw.next = self.head
+            self.head = nw
+
 
     def pop(self):
+        if self.head is not None:
+            ppn = self.head
+            self.head = self.head.next
+            ppn.next = None
+            return ppn.data
+        else:
+            return None
 
 a_stack = Stack()
 while True:

Exercise_3.py

@@ -2,7 +2,12 @@ class ListNode:
     """
     A node in a singly-linked list.
     """
-    def __init__(self, data=None, next=None):
+
+    def __init__(self, data, next=None):
+        self.data = data
+        self.next = next
+
+
 
 class SinglyLinkedList:
     def __init__(self):
@@ -13,20 +18,68 @@ def __init__(self):
         self.head = None
 
     def append(self, data):
+
+        if self.head == None: 
+            self.head = ListNode(data)
+            return
+
+        curr = self.head
+        while curr.next:
+                curr = curr.next
+        curr.next = ListNode(data)    
+
+
+
+
         """
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
 
     def find(self, key):
+
+        curr = self.head
+        while (curr):
+            if (curr.data == key):
+                return curr
+
+            curr = curr.next
+        return None
         """
         Search for the first element with `data` matching
         `key`. Return the element or `None` if not found.
         Takes O(n) time.
         """
 
     def remove(self, key):
+        if self.head and self.head.data == key:
+            temp = self.head
+            self.head = self.head.next
+            temp.next = None
+            return
+
+        curr = self.head
+        while curr and curr.next:
+            if (curr.next.data == key):
+                temp = curr.next 
+                curr.next = curr.next.next
+                temp.next = None 
+                return
+            curr = curr.next
+        return None 
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+    def print_list(self):
+        curr = self.head
+
+        if curr is None:
+            print("List is empty")
+            return
+
+        while curr:
+            print(curr.data, end=" -> ")
+            curr = curr.next
+        print("None")
+