Completed PreCourse-1

Exercise_1.py

@@ -1,20 +1,34 @@
 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 size(self):
-
-     def show(self):
+  def __init__(self):
+    self.stack = []
+
+  def isEmpty(self):
+    if len(self.stack) > 0:
+      return False
+    return True
+
+  def push(self, item):
+    self.stack.append(item)
+
+  def pop(self):
+    if len(self.stack)  == 0:
+      return 'Sorry we dont have any value in stack'
+    popped_val = self.stack[-1]
+    self.stack = self.stack[:-1]
+    return popped_val
+
+  def peek(self):
+    if len(self.stack)  == 0:
+      return 'Sorry we dont have any value in stack'
+    return self.stack[-1]
+
+  def size(self):
+    return len(self.stack)
+
+  def show(self):
+    return self.stack
 
 
 s = myStack()

Exercise_2.py

@@ -6,10 +6,39 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.node = None
 
     def push(self, data):
+        if self.node:
+            flag = True
+            last_node = self.node
+            while(flag):
+                if not last_node.next:
+                    last_node.next = Node(data)
+                    flag = False 
+                else:
+                    last_node = last_node.next
+        else:
+            self.node = Node(data)
+        print('Data is added %s'%data)
 
     def pop(self):
+        popped_val = None
+        if self.node:
+            flag = True
+            last_node = self.node
+            while(flag):
+                if not last_node.next:
+                    popped_val = last_node.data
+                    self.node = None
+                    flag = False 
+                elif not last_node.next.next:
+                    popped_val = last_node.next.data
+                    last_node.next = None
+                    flag = False 
+                else:
+                    last_node = last_node.next
+        return popped_val
 
 a_stack = Stack()
 while True:

Exercise_3.py

@@ -3,30 +3,66 @@ 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):
         """
         Create a new singly-linked list.
         Takes O(1) time.
         """
-        self.head = None
+        self.head = ListNode(None)
+
+    def print_val(self):
+        """
+        Helper function to debug
+        """
+        last_node = self.head
+        while(last_node):
+            print(last_node.data)
+            last_node = last_node.next
 
     def append(self, data):
         """
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        if not self.head.data:
+            self.head.data = data
+            return 
+        last_node = self.head
+        while(last_node.next):
+            last_node = last_node.next
+        last_node.next = 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 not self.head:
+            return False
+        last_node = self.head
+        while(last_node):
+            if last_node.data == key:
+                return True
+            last_node = last_node.next
+        return False
+
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        last_node = self.head
+        if last_node.data == key:
+           self.head = last_node.next
+           return True
+        while(last_node.next):
+            if last_node.next.data == key:
+                last_node.next = last_node.next.next 
+                return True
+            last_node = last_node.next
+        return False