precourse - 1 harika

Exercise_1.py

@@ -2,20 +2,27 @@ 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 = []
+
 
      def isEmpty(self):
-
+        if len(self.stack) == 0:
+           return self.stack
+
      def push(self, item):
-
+         return self.stack.append(item)
      def pop(self):
-
-        
+        return self.stack.pop()
+
      def peek(self):
+        return self.stack[len(self.stack) -1]
 
      def size(self):
+        return len(self.stack)
 
      def show(self):
-
+        for i in range(len(self.stack)):
+           return self.stack[i]
 
 s = myStack()
 s.push('1')

Exercise_2.py

@@ -6,10 +6,12 @@ def __init__(self, data):
 
 class Stack:
     def __init__(self):
-
+        self.stack = []
+
     def push(self, data):
-
+        self.append(data)
     def pop(self):
+        return self.pop()
 
 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 +19,42 @@ def append(self, data):
         Insert a new element at the end of the list.
         Takes O(n) time.
         """
+        new = ListNode(data)
+        if self.head == None:
+            self.head = new
+            new.next = None
+        curr = self.head
+        while curr.next != None:
+            curr = curr.next
+        curr.next = new
 
     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
+        while curr != None:
+            if curr.data == key:
+                return curr
+        return None
+
     def remove(self, key):
         """
         Remove the first occurrence of `key` in the list.
         Takes O(n) time.
         """
+        if self.head == key:
+            self.head = self.head.next
+            return
+        prev = self.head
+        curr = self.head.next
+        while curr.next != None:
+            if curr.data == key:
+                prev.next = curr.next
+            prev = prev.next
+            curr = curr.next
+
+
+