Precourse Ex1

Exercise_1.py

@@ -1,21 +1,35 @@
+# Time Complexity : O(1) for all operations
+# Space Complexity : O(n) - n is size
+# Did this code successfully run on Leetcode : Ran on terminal
+# Any problem you faced while coding this : NA
+
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+      self.myStack=[]
 
      def isEmpty(self):
+      return len(self.myStack)==0
 
      def push(self, item):
+      self.myStack.append(item)
 
      def pop(self):
-
+        if self.isEmpty():
+          return "Stack is Empty"
+        return self.myStack.pop()
 
      def peek(self):
-
+        if self.isEmpty():
+          return "Stack is Empty"
+        return self.myStack[-1]
+
      def size(self):
+         return len(self.myStack)
 
      def show(self):
-
+         return self.myStack
 
 s = myStack()
 s.push('1')

Exercise_2.py

@@ -1,3 +1,5 @@
+# Time Complexity : O(1) for all operations
+# Space Complexity : O(n) - n is size
 
 class Node:
     def __init__(self, data):
@@ -6,10 +8,20 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.top = None
 
     def push(self, data):
+        new_item = Node(data)
+        new_item.next = self.top
+
+        self.top = new_item
 
     def pop(self):
+        if self.top == None:
+            return None
+        popped = self.top
+        self.top = popped.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=next
 
 class SinglyLinkedList:
     def __init__(self):
@@ -17,16 +19,49 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        new_item = ListNode(data)       
+        curr = self.head
+        #If empty set the head
+        if curr is None:
+            self.head = new_item
+            return 
+
+        #Traverse to the end and point last element's next to the new node
+        while curr.next:
+            curr = curr.next
+        curr.next = new_item
 
     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.
         """
+        curr = self.head
+        # Traverse until data is found
+        while curr:
+            if curr.data == key:
+                return curr
+            curr=curr.next
+        return None
 
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        curr = self.head
+        if curr is None:
+            return
+        if curr.data == key:
+            self.head = curr.next
+            return 
+        #Traverse to find the element but keep the poointer one step back so we can change the next pointer 
+        while curr.next:
+            if curr.next.data == key:
+                curr.next = curr.next.next
+                return 
+            curr=curr.next
+        return None
+
+