Precourse 1 - completed

Exercise_1.py

@@ -1,24 +1,78 @@
+
+### Stack with array
+
+
 class myStack:
   #Please read sample.java file before starting.
   #Kindly include Time and Space complexity at top of each file
      def __init__(self):
+         self.stack = []
+         self.MAX = 5
+
+
+     def size(self):
+         return len(self.stack)
+         #Time complexity O(1)
+
 
      def isEmpty(self):
+         if self.size()==0:
+             return True
+         else:
+            return False
+          #Time complexity O(1)
+
 
      def push(self, item):
+         if self.size()!=self.MAX:
+             self.stack.append(item)
+         else:
+             print("Stack is full")
+         return self.stack
+         #Time complexity O(1)
+
 
      def pop(self):
+         if not self.isEmpty():
+             p=self.stack.pop()
+             return p
+         else:
+             print("Stack is empty")
+             return None
+          #Time complexity O(1)
+
 
 
      def peek(self):
-
-     def size(self):
+         if not self.isEmpty():
+             return self.stack[-1]
+         else:
+             return None
+          #Time complexity O(1)
+
 
      def show(self):
-
+         return self.stack
+         #Time complexity O(1)
+# Space Complexity: O(n)     
 
 s = myStack()
 s.push('1')
 s.push('2')
+s.push('3')
+s.push('4')
+s.push('5')
+s.push('6')
+
+
+print(s.pop())
+print(s.pop())
+print(s.pop())
 print(s.pop())
+
+
+
 print(s.show())
+print(s.peek())
+
+

Exercise_2.py

@@ -6,10 +6,26 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
+        self.top = None
+        self.count = 0
 
     def push(self, data):
-
+        new_node = Node(data)
+        new_node.next = self.top
+        self.top = new_node
+        self.count+=1
+         #Time complexity O(1)
+
     def pop(self):
+        if self.top == None:
+            return None
+        else:
+            p = self.top.data
+            self.top = self.top.next
+            self.count -=1
+            return p
+         #Time complexity O(1)
+  #Space complexity O(n)                   
 
 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):
@@ -11,22 +13,54 @@ def __init__(self):
         Takes O(1) time.
         """
         self.head = None
+
 
     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 == 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.data
+            current = current.next
+        return None
+
+
 
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+
+        current = self.head
+        previous_node = None
+
+        while current:
+            if current.data == key:
+                if previous_node:
+                    previous_node.next=current.next
+                    return
+                else:
+                    self.head = current.next
+            previous_node = current
+            current=current.next