Pre-course - 1 complete

Exercise_1.py

@@ -1,21 +1,44 @@
+# Time Complexity : O(1)
+# Space Complexity : O(N)
+# Did this code successfully run on Leetcode : Ran it locally
+# Any problem you faced while coding this : Deciding the max length and adding the sanity checks
+
+
+# Your code here along with comments explaining your approach
 class myStack:
-  #Please read sample.java file before starting.
-  #Kindly include Time and Space complexity at top of each file
      def __init__(self):
-
+        self.maxLen = 1000                    # Maximum length allowed for the stack
+        self.stack = []                       # Array that will be used as stack
+        self.length = 0                       # length for O(1) access to check the length
+
      def isEmpty(self):
+          if self.length == 0:                # If the stack is empty then the length will be zero
+               return True
+          return False
 
      def push(self, item):
+          if self.length == self.maxLen:      # If the length has reached the max allowed length then reject the push
+              return "Stack is full"
+          self.stack.append(item)
+          self.length += 1
 
      def pop(self):
+        if self.length == 0:                  # If the stack is empty then reject the pop
+             return "Stack is empty!"
 
+        self.length -= 1
+        return self.stack.pop()
 
      def peek(self):
-
-     def size(self):
-
-     def show(self):
+        if len(self.stack) == 0:              # If the stack is empty reject the peek as there is no item to peek
+             return "Stack is empty!"
+        return self.stack[-1]
+
+     def size(self):                          # Return the size of the stack
+         return self.length
 
+     def show(self):                          # Return the entire stack
+         return self.stack
 
 s = myStack()
 s.push('1')

Exercise_2.py

@@ -1,15 +1,39 @@
+# Time Complexity : O(1)
+# Space Complexity : O(N)
+# Did this code successfully run on Leetcode : Ran it locally
+# Any problem you faced while coding this : Forgot what actually stack means and build a queue using linkedlist
+# Staying focussed and aware is what I need to improve on.
+# Learned to write comments using ''''''
 
+
+# Your code here along with comments explaining your approach
 class Node:
     def __init__(self, data):
        self.data = data
        self.next = None
 
 class Stack:
     def __init__(self):
+        '''Create an empty pointer to store the top of the linked list/stack'''
+        self.linkedListTop = None
 
     def push(self, data):
-
+        '''Creating a node with the data to add to the top of the linked list'''
+        dataNode = Node(data)
+        if self.linkedListTop is None:
+            self.linkedListTop = dataNode
+        else:
+            '''Adding datanode to the top of the linked list and setting the linkedListTop to it'''
+            dataNode.next = self.linkedListTop
+            self.linkedListTop = dataNode
+
     def pop(self):
+        if self.linkedListTop is  None:
+            return None
+        '''Removing the top node and setting linkedListTop to the next node in the list'''
+        poppedData = self.linkedListTop.data
+        self.linkedListTop = self.linkedListTop.next
+        return poppedData
 
 a_stack = Stack()
 while True:

Exercise_3.py

@@ -1,8 +1,17 @@
+# Time Complexity : O(N) for all operations
+# Space Complexity : O(N)
+# Did this code successfully run on Leetcode : Ran it locally
+# Any problem you faced while coding this : None
+
+
+# Your code here along with comments explaining your approach
 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 +26,92 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        node = ListNode(data=data)
+        '''If the linkedlist is empty set the head to the node'''
+        '''Else iterate the linkedlist to reach the end of the list and attach the node'''
+
+        if self.head is None:
+            self.head = node
+
+        else:
+            curr = self.head
+
+            while curr.next:
+                curr = curr.next
+
+            curr.next = 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.
         """
+        curr = self.head
+        '''Iterate the linkedlist to find the key'''
+        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.
         """
+
+        '''If the key is the first node then update the head to head.next'''
+        if self.head.data == key:
+            curr = self.head
+            self.head = self.head.next
+            return curr
+
+        '''Iterate the linkedlist and link the node before the key with the node after the key'''
+        curr = self.head
+        prev = self.head
+        while curr:
+            if curr.data == key:
+                prev.next = curr.next
+                return curr
+            prev = curr
+            curr = curr.next
+
+    def show(self):
+        curr = self.head
+        result = []
+        while curr:
+            result.append(curr.data)
+            curr = curr.next
+        return result
+
+
+a_stack = SinglyLinkedList()
+while True:
+    print('Linked List: ', a_stack.show())
+    #Give input as string if getting an EOF error. Give input like "push 10" or "find 10"
+    print('push <value>')
+    print('find <value>')
+    print('remove <value>')
+    print('quit')
+    do = input('What would you like to do? ').split()
+    #Give input as string if getting an EOF error. Give input like "push 10" or "pop"
+    operation = do[0].strip().lower()
+    if operation == 'push':
+        a_stack.append(int(do[1]))
+    elif operation == 'find':
+        popped = a_stack.find(int(do[1]))
+        if popped is None:
+            print('Element not found')
+        else:
+            print('Element found: ', popped.__str__)
+    elif operation == 'remove':
+        popped = a_stack.remove(int(do[1]))
+        if popped is None:
+            print('Element not found')
+        else:
+            print('Element removed successfully')
+    elif operation == 'quit':
+        break