Completed s30 PreCourse-1

Exercise_1.py

@@ -1,24 +1,49 @@
 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 __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"
+        else:
+            return self.stack.pop()
+
+      def peek(self):
+         if self.isEmpty():
+            return "Stack is empty"
+         else:
+            return self.stack[-1]
+
 
-     def size(self):
+      def size(self):
+         return len(self.stack)
 
-     def show(self):
+      def show(self):
+         return self.stack
 
 
 s = myStack()
 s.push('1')
 s.push('2')
 print(s.pop())
 print(s.show())
+
+'''
+Time Complexity : O(1)
+push() : O(1)
+pop() :	O(1)
+peek() : O(1)
+isEmpty() : O(1)
+size() : O(1)
+show() : O(1)	
+
+Space Completxity : O(n)
+'''

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_node = self.top
+        self.top = self.top.next
+        return popped_node.data
 
 a_stack = Stack()
 while True:
@@ -30,3 +40,12 @@ def pop(self):
             print('Popped value: ', int(popped))
     elif operation == 'quit':
         break
+
+'''
+Time Complexity : O(1)
+Push  : O(1)
+Pop   : O(1)
+Peek  : O(1)
+
+Space Complexity : O(n)
+'''

Exercise_3.py

@@ -3,6 +3,9 @@ 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 +20,61 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        new_node = ListNode(data)
+
+        if self.head is None:
+            self.head = new_node
+            return
+
+        current = self.head
+        while current.next:
+            current = current.next
+        current.next = new_node
 
     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.
         """
+        if self.head is None:
+            return
+
+        if self.head.data == key:
+            self.head = self.head.next
+            return
+
+        prev = self.head
+        current = self.head.next
+
+        while current:
+            if current.data == key:
+                prev.next = current.next
+                return
+            prev = current
+            current = current.next
+
+'''
+Time Complexity : O(n) 
+append	: O(n)
+find :	O(n)
+remove : O(n)
+
+Space Complexity : O(n)
+
+'''