Completed PreCourse-1 Exercises

Exercise_1.py

@@ -1,20 +1,40 @@
+'''
+Time Complexity : O(1)
+Space Complexity : O(1)
+Did this code successfully run on Leetcode : Yes, but the question on leetcode was using Queues and not Arrays
+Any problem you faced while coding this : No
+
+'''
+
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
-     def __init__(self):
+  def __init__(self):
+    self.storage = []
 
-     def isEmpty(self):
+  def isEmpty(self):
+    if len(self.storage) == 0:
+      return True
+    return False
 
-     def push(self, item):
 
-     def pop(self):
-
+  def push(self, item):
+    self.storage.append(item)
+
+  def pop(self):
+    if not self.isEmpty():
+      self.storage.pop()
 
-     def peek(self):
 
-     def size(self):
+  def peek(self):
+    if not self.isEmpty():
+      return self.storage[-1]
+
+  def size(self):
+    return len(self.storage)
 
-     def show(self):
+  def show(self):
+    return self.storage
 
 
 s = myStack()

Exercise_2.py

@@ -6,10 +6,19 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.head = None
 
     def push(self, data):
+        new_node = Node(data)
+        new_node.next = self.head
+        self.head = new_node
 
     def pop(self):
+        if self.head is None:
+            return None
+        temp = self.head
+        self.head = self.head.next
+        return temp.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 = None
 
 class SinglyLinkedList:
     def __init__(self):
@@ -17,16 +19,48 @@ 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
+        else:
+            current = self.head
+            while current.next != None:
+                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.
         """
+        if self.head is None:
+            return None
+        else:
+            current = self.head
+            while(current.data != key and current.next != None):
+                current = current.next
+            if current.data == key:
+                return current.data
+        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 None
+        else:
+            current = self.head
+            if current.data == key:
+                temp = self.head
+                self.head = self.head.next
+                temp.next = None
+            else:
+                while(current.next.data != key and current.next!=None):
+                    current = current.next
+                if current.next.data == key:
+                    current.next = current.next.next
+                else:
+                    return None