Completed PreCourse 1

Exercise_1.py

@@ -1,21 +1,57 @@
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
+
+  #Time and Space Complexity
+  # Overall Space Complexity = O(N) where N is the MAX_SIZE of 1000
+  # __init__ function has the time and space complexity of O(N)
+  # isEmpty function has the time and space complexity of O(1)
+  # push function has the time and space complexity of O(1)
+  # pop function has the time and space complexity of O(1)
+  # peek function has the time and space complexity of O(1)
+  # size function has the time and space complexity of O(1)
+  # show function has the time and space complexity of O(M) where M dentoes the number of elements in the stack
+
+
      def __init__(self):
+          self.MAX_SIZE=1000
+          self.array=[None]*self.MAX_SIZE
+          self.top=-1
 
      def isEmpty(self):
+          if self.top==-1:
+               return True
+          return False
 
      def push(self, item):
+          if self.top<self.MAX_SIZE-1:
+            self.top+=1
+            self.array[self.top]=item
+          else:
+            print("Stack Overflow")
+            return False
 
      def pop(self):
-
-
+          if self.top>-1:
+            value=self.array[self.top]
+            self.top-=1
+            return value
+          else:
+            print("Stack Underflow")
+            return False
+
      def peek(self):
+         if self.top==-1:
+             return False
+         else:
+             return self.array[self.top]
 
      def size(self):
+         return self.top+1
 
      def show(self):
-
+         return self.array[0: self.top+1][::-1]  
+
 
 s = myStack()
 s.push('1')

Exercise_2.py

@@ -1,15 +1,29 @@
-
+# Time and Space Complexity
+# Overall Space Complexity is O(N) where N is the number of elements in stack
+# __init__ function has time and space complexity of O(1)
+# push function has time and space complexity of O(1)
+# pop function has time and space complexity of O(1)
 class Node:
     def __init__(self, data):
        self.data = data
        self.next = None
 
 class Stack:
     def __init__(self):
+        self.top=None
 
     def push(self, data):
+        newNode=Node(data)
+        newNode.next=self.top
+        self.top=newNode
 
     def pop(self):
+        if self.top==None:
+            return None
+        else:
+            value=self.top.data
+            self.top=self.top.next
+            return value
 
 a_stack = Stack()
 while True:

Exercise_3.py

@@ -1,8 +1,16 @@
+# Time and Space Complexity
+# Overall Space Complexity is O(N) where N is total number of elements in the list
+# append function takes O(N) time complexity and O(1) space complexity
+# find function takes O(N) time complexity and O(1) space complexity
+# remove function takes O(N) time complexity and O(1) space complexity
+
 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):
@@ -17,16 +25,50 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        newNode=ListNode(data)
+        if self.head==None:
+            self.head=newNode
+        else:
+            a=self.head
+            while a.next!=None:
+                a=a.next
+            a.next=newNode
 
     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.
         """
+        a=self.head
+        while a!=None:
+            if a.data==key:
+                return a 
+            a=a.next 
+        return None 
 
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        a=self.head
+        if self.head==None:
+            return None 
+        if self.head.data==key:
+            self.head=self.head.next 
+            return None 
+        while a.next!=None:
+            if a.next.data==key:
+                a.next=a.next.next
+                return None 
+            a=a.next 
+
+ll = SinglyLinkedList()
+
+ll.append(10)
+ll.append(20)
+ll.append(30)
+found = ll.find(20)
+print(found.data)
+ll.remove(20)