accepts strings from user and generates stack till it gets the input "End"
Next, it should sort the given stack in a decent order
Finally, print the sorted stack
I cannot seem to get the logic right using only push and pop methods whereby push is a function putting elements to the top of the stack and pop is a function removing the top element of the stack and storing it. I am only allowed to use push and pop, the sorting algorithm is the only one I cant do.
from Stack import Stack
def display_(S_):
node = S_.list.head
while node != None:
print(node.data)
node = node.next
def Sorting_Stack(stack,k):
v = 0
ar = 0
temp = Stack()
for i in range(k):
v = stack.pop()
temp.push(v)
node = stack.list.head
tnode = temp.list.head
if tnode.data > node.data:
ar = temp.pop()
stack.push(ar)
display_(stack)
if __name__ == '__main__':
stack = Stack()
string = ""
k = 0
while string!='End':
string = input()
if string == 'End':
break
else:
stack.push(string)
k += 1
Sorting_Stack(stack, k)
#this is Stack.py--------
from Node import Node
from LinkedList import LinkedList
class Stack:
def __init__(self):
self.list = LinkedList()
def push(self, new_item):
# Create a new node to hold the item
new_node = Node(new_item)
# Insert the node as the list head (top of stack)
self.list.prepend(new_node)
def pop(self):
# Copy data from list's head node (stack's top node)
popped_item = self.list.head.data
# Remove list head
self.list.remove_after(None)
# Return the popped item
return popped_item
#Stack Class
class Stack:
def __init__(self):
self.stack = []
def push(self,item):
if item == 'End':
self.sort()
else:
self.stack.append(item)
def pop(self):
if len(self.stack) == 0:
print("Stack Is Empty")
else:
self.stack.pop()
def sort(self):
self.stack.sort()
print(self.stack)
logic For giving Inputs
s = Stack()
item = None
while item !='End':
print("Type 'End' For Ending the Stack Push Operation")
item = input("Enter Item: ")
s.push(item)
s.push(item)
Program will take inputs till we give input as 'End'.
After given 'End' as Input it will sort the stack and print it.
Related
I am having some trouble with linked lists in Python. For a problem I am supposed to do trivia like question and answer with linked lists, each node having a question and answer. I am supposed to have the program go through the list over and over until each question is answered correctly twice. The following code is the method I made to do this.
class trivia(object):
def __init__(self, question, answer):
self.question = question
self.answer = answer
self.next = None
def getQuestion(self):
return self.question
def getAnswer(self):
return self.answer
def getNext(self):
return self.next
def setNext(self, next):
self.next = next
class triviaDeck(object):
def __init__(self):
self.head = None
def size(self):
current = self.head
count = 0
while current != None: # while not at the end of the list
count += 1
current = current.getNext()
return count
def showTrivia(self, pos=None):
if pos == None:
pos = self.size() - 1
if pos < self.size() and pos >= 0:
current = self.head
previous = None
index = 0
count = 0
while count != 2:
print(current.getQuestion())
answer = input()
if answer == current.getAnswer():
print("Correct")
count = count + 1
if current.getNext() == 2:
current = self.head
else:
current = current.getNext()
def add(self, question, answer):
temp = trivia(question, answer)
temp.setNext(self.head)
self.head = temp
if __name__ == '__main__':
deck = triviaDeck()
deck.add("A", "A")
deck.add("B", "B")
deck.add("C", "C")
deck.showTrivia()
Currently this code just goes through the list once and then exits.
For a circular linked list:
The first node inserted should point to itself
For additional nodes, adjust the pointers to insert the new node after the head
Try this code:
def add(self, question, answer):
temp = trivia(question, answer)
if not self.head: # first node
self.head = temp
temp.setNext(self.head) # single node, loop to itself
else: # add node
temp.setNext(self.head.getNext()) # shift loop
self.head.setNext(temp) # insert just after head
Also - For the count = 2 logic:
The node (trivia) object should have a counter property which counts correct responses to that question
If the response counter = 2, remove that node from the linked list
When the last node is removed, game over
Attempting to create a method for a singly linked list and struggling to understand why this test case is failing. In my second class SLinkedList, I have a method called insert, it takes the argument pos which is an integer. Now in my test case when I add middle to position 4 it stops referencing any further nodes the linked list meaning that the node containing the data middle does not have a reference to the node containing 77. I'm confused why this is happening? I've programmed it such that when current_pos==pos we set the next of our current (new_node) to be current.getNext() (77). Haven't I assigned the next of 2 to middle and the next of middle to 77?
class SLinkedListNode:
# an instance of this class is a node in a Single Linked List
# a node has a reference to data and reference to next
def __init__(self,initData,initNext):
self.data = initData
self.next = initNext
def getNext(self):
return self.next
def getData(self):
return self.data
def setData(self,newData):
self.data = newData
def setNext(self,newNext):
self.next = newNext
class SLinkedList:
# an instance of this class is a Singly-Linked List object
# it has reference to the first node in the list
def __init__(self):
self.head = None
self.size = 0
def add(self,item):
# adds an item at the start of the list
new_node = SLinkedListNode(item,None)
new_node.setNext(self.head)
self.head = new_node
self.size = self.size + 1
def append(self,item):
# adds an item at the end of the list
new_node = SLinkedListNode(item,None)
current = self.head # Start the traversal
if self.size == 0: # check if list is empty
self.add(item)
else:
while (current.getNext()!=None):
current= current.getNext() # traversing the list
current.setNext(new_node)
self.size = self.size +1
def insert(self,pos,item):
# inserts the item at pos
# pos should be a positive number (or zero) of type int
assert type(pos)==int,'Error:pos is not an integer'
assert pos>=0,'Error:pos must be positive'
current=self.head
new_node= SLinkedListNode(item,None)
if pos==0:
self.add(item)
elif pos==self.size:
self.append(item)
else:
current_pos=0
while(current.getNext()!=None):
if (pos-1)==current_pos:
print(current.getData())
current.setNext(new_node)
if pos==current_pos:
print(current.getData())
new_node.setNext(current.getNext())
current=current.getNext()
current_pos+=1
self.size+=1
# 1--> 2--->inserteditem---> 3-->4---> 5---> 6
# TO DO: write assert statement that tests if pos is int
# TO DO: write assert statement that tests that pos is not negative
# TO DO: COMPLETE THE METHOD
def remove(self,item):
# remove the node containing the item from the list
if self.size == 0:
raise Exception('List is Empty')
current = self.head
previous = None
found = False
while current != None and not found:
if current.getData() == item:
found = True
else:
previous = current
current = current.getNext()
if not found:
raise Exception('Item not in list')
else:
if previous == None: # the item is in the first node of the list
self.head = current.getNext()
else: # item is not in the first node
previous.setNext(current.getNext())
self.size = self.size -1
def index(self,item):
# finds the location of the item in the list
if self.size == 0:
raise Exception('List is empty')
position = 0
found = False
current = self.head
while current != None and not found:
if current.getData() == item:
found = True
else:
current = current.getNext()
position = position + 1
if found:
return position
else:
return 'Item not found'
def pop(self):
# removes the node from the end of the list and returns the item
if self.size == 0:
raise Exception('List is empty')
current = self.head
previous = None
while current.getNext() != None:
previous = current
current = current.getNext()
if previous == None:
self.head = None
else:
previous.setNext(None)
self.size = self.size -1
return current.getData()
def __str__(self):
# returns a string representation of the list
current = self.head
string = ''
while current != None:
string = string + str(current.getData())+'->'
current = current.getNext()
return string
def getSize(self):
return self.size
def main():
# Testing Singly-Linked List
slist = SLinkedList()
slist.add(2)
slist.add(4)
slist.add('A')
slist.append(77)
slist.append(6)
slist.append('Z')
print('Original List:', slist.getSize(), 'elements')
print(slist)
print()
slist.insert(0,'start')
print('After inserting the word start at position 0:', slist.getSize(), 'elements')
print(slist)
print()
slist.insert(7,'end')
print('After inserting the word end at position 7:', slist.getSize(), 'elements')
print(slist)
print()
slist.insert(4,'middle')
print('After inserting middle at position 4:', slist.getSize(), 'elements')
print(slist)
if __name__=="__main__":
main()
Take a look at this code snippet from your insert-method:
else:
current_pos=0
while(current.getNext()!=None):
if (pos-1)==current_pos:
print(current.getData())
current.setNext(new_node)
if pos==current_pos:
new_node.setNext(current.getNext())
current=current.getNext()
current_pos+=1
Once the first if-condition is met, you're setting your new node as the current node's next node. Bear in mind, this new node has no reference to the rest of the list. The second if statement will not execute during this iteration, so the next line to be executed is current=current.getNext(), which sets current to be your new node, still without reference to the rest of the list. Therefore, in the next iteration of the while loop current.getNext() evaluates to None and your iteration terminates right then and there, effectively removing all nodes after your new node from the list.
To fix this, remove the second if and set the new node's next node in the previous if statement. This way, you'll maintain the reference to the rest of the list.
On a side note, get- and set-methods are very unpythonic, you can access and modify these attributes directly, e.g. by using current.next = whatever. Also, a while-loop iterating over your entire list seems fairly inefficient for the insert task since you exactly know the index to insert the new node into. Also also, your insert-method will break for positions greater than the list's length, you might want to add another check for that
Given a linked list, write a function to reverse every k nodes (where k is an input to the function).
Examples:
Inputs: 1->2->3->4->5->6->7->8->NULL and k = 3
Output: 3->2->1->6->5->4->8->7->NULL.
Inputs: 1->2->3->4->5->6->7->8->NULL and k = 5
Output: 5->4->3->2->1->8->7->6->NULL.
This is the Code:
# Node class
class Node:
# Constructor to initialize the node object
def __init__(self, data):
self.data = data
self.next = None
class LinkedList:
# Function to initialize head
def __init__(self):
self.head = None
def reverse(self, head, k):
current = head
Next = None
prev = None
count = 0
# Reverse first k nodes of the linked list
while(current is not None and count < k):
Next = current.next
current.next = prev
prev = current
current = Next
count += 1
# next is now a pointer to (k+1)th node
# recursively call for the list starting
# from current . And make rest of the list as
# next of first node
if Next is not None:
head.next = self.reverse(Next, k)
# prev is new head of the input list
return prev
# Function to insert a new node at the beginning
def push(self, new_data):
new_node = Node(new_data)
new_node.next = self.head
self.head = new_node
# Utility function to print the linked LinkedList
def printList(self):
temp = self.head
while(temp):
print temp.data,
temp = temp.next
# Driver program
llist = LinkedList()
llist.push(9)
llist.push(8)
llist.push(7)
llist.push(6)
llist.push(5)
llist.push(4)
llist.push(3)
llist.push(2)
llist.push(1)
print "Given linked list"
llist.printList()
llist.head = llist.reverse(llist.head, 3)
print "\nReversed Linked list"
llist.printList()
On my computer, this code gives me error saying "LinkedList class has no attribute next" => the error in this statement "Next = current.next" . On Geeks for Geeks the code is running fine. Also on all the online IDEs the code is running fine. So is it something wrong with my device or the code should not run ?
I have looked at many very similar questions and cannot figure it out so:
I have a string like this:
{121{12}12{211}2}
I want to read the string into a tree like this:
I am confused as how to tell python to add a whole list as a child node?
I would also like to know how to change the current node to the parent of the old current node?
Here is my code so far:
class Node:
def __init__(self,val):
self.value = val
self.children = []
#init Node class so we can pass in values as nodes and set children to empty list
def add_child(self, obj):
self.children.append(obj)
s=[]
for i in filedata:
if i == leftbrace:
n = Node(i)
#create new child of current node
s = []
#reset list s to blank
if i == rightbrace:
n.add_child(s)
#add list s to current node
#make parent of current node the new current node
else:
s.append(i)
#add i to list s
for c in n.children:
print (c.data)
To make something like this work, it is easiest if you use recursion. Here is one way that this can be done.
Code:
class Node:
def __init__(self, stream):
val = []
children = []
while True:
try:
# get the next character from the stream
ch = next(stream)
# if this is an open brace, then recurse to a child
if ch == '{':
children.append(Node(stream))
# if this is a close brace, we are done on this level
elif ch == '}':
break
# otherwise add this character to our value
else:
val.append(ch)
# stream is empty, we are done
except StopIteration:
break
self.value = ''.join(val)
self.children = children
#classmethod
def from_string(cls, string):
stream = iter(string)
tree_top = Node(stream)
# assert that the string started with '{' and was one top node
assert len(tree_top.children) == 1 and tree_top.value == ''
return tree_top.children[0]
def __str__(self):
return self.value
def __repr__(self):
return "Node('%s', <%d children>)" % (
self.value, len(self.children))
def tree_string(self, level=0):
yield '-' + " " * level + str(self)
for child in self.children:
for child_string in child.tree_string(level+1):
yield child_string
tree = '{121{12}12{211}2}'
for line in Node.from_string(tree).tree_string():
print(line)
Results:
-121122
- 12
- 211
So i was given this question. Consider the Stack and the Queue class with standard set of operations. Using the Stack and Queue class, what items are contained in them just before the mysteryFunction is called AND just after the mysteryFunction is called?
Here is the code:
def mysteryFunction(s, q):
q.enqueue('csc148')
q.enqueue(True)
q.enqueue(q.front())
q.enqueue('abstract data type')
for i in range(q.size()):
s.push(q.dequeue())
while not s.is_empty():
q.enqueue(s.pop())
if __name__ == '__main__':
s=Stack()
q=Queue()
#About to call mysteryFunction
#What are contents of s and q at this point?
mysteryFunction(s, q)
#mysteryFunction has been called.
#What are contents of s and q at this point?
I'm having trouble understanding object oriented programming as i'm new to this topic. Is there any link that breaks down Stacks and Queues and what they do?
In general, stacks are LIFO and queues are FIFO.
In Python, you can use the collections module to experiment with stacks and queues:
>>> from collections import deque
>>> stack = deque()
>>> stack.append(10)
>>> stack.append(20)
>>> stack.append(30)
>>> stack
deque([10, 20, 30])
>>> stack.pop() # LIFO
30
>>> stack.pop()
20
>>>
>>> queue = deque()
>>> queue.append(10)
>>> queue.append(20)
>>> queue.append(30)
>>> queue
deque([10, 20, 30])
>>> queue.popleft() # FIFO
10
>>> queue.popleft()
20
See following links for more information:
Stack
Queue
Visually these two data structures can be seen in a following way:
Stack:
Description:
There are variations of this data structure. However, in simple terms - as one can observe in the image provided, when you add to this data structure you place on top of what is already there and when you remove you also take from the top. You can view it as a stack of books which you go through one by one starting from the top and all the way down.
Queue
Description:
There are also variations on this particular data structure, however in simple terms - as you can see in the image provided, when you add to this data structure the new element goes in the begining and when you remove its the last element from the list which is being removed. You can imagine it as a queue you got in a shop where you stand behind a lot of people waiting for your turn to come to the counter to pay for your items.
To test this line by line, here are implementations of the classes (wrappers around deque) that are used in the task:
from collections import deque
class Queue(deque):
enqueue = deque.append
dequeue = deque.popleft
def front(self):
return self[-1]
def size(self):
return len(self)
class Stack(deque):
push = deque.append
def is_empty(self):
return not self
STACK #LIFO
class stack(object):
def __init__(self):
self.items = []
def isEmpty(self):
return self.items==[]
def push(self,item):
self.items.append(item)
def pop (self):
return self.items.pop()
def peek(self):
return self.items[len(self.items) - 1]
def size(self):
return (len(self.items))
s = stack()
print (s.isEmpty())
>> True
s.push(1)
s.push('3')
s.peek()
>>'3'
s.size()
>> 2
Queue #FIFO
class Queue(object):
def __init__(self):
self.items = []
def isEmpty(self):
return self.items==[]
def enqueue(self,item):
self.items.insert(0,item)
def dequeue(self):
return self.items.pop()
def size(self):
return (len(self.items))
q = Queue()
q.isEmpty()
>>True
q.enqueue(1)
q.enqueue(2)
q.dequeue()
>>1
The first code explains about the stack , we need to create a list and while pushing the element use append and fill the list , similar to what we have in array stack. While pop , pop out the end from where you pushed it.
class Stack:
def __init__(self):
self.stack = []
def push_element(self,dataval):
self.stack.append(dataval)
return self.stack
def pop_element(self):
if len(self.stack) ==0:
print("Stack is empty")
else:
self.stack.pop()
return self.stack
def peek_element(self):
return self.stack[0]
class Queue:
def __init__(self):
self.stack = []
def push_ele(self,data):
self.stack.append(data)
def pop_ele(self):
self.stack.pop(0)
def display(self):
print(self.stack)
class stack:
def __init__(self,n): #constructor
self.no = n # size of stack
self.Stack = [] # list for store stack items
self.top = -1
def push(self): # push method
if self.top == self.no - 1: # check full condition
print("Stack Overflow.....")
else:
n = int(input("enter an element :: "))
self.Stack.append(n) # in list add stack items use of append method
self.top += 1. # increment top by 1
def pop(self): # pop method
if self.top == -1: # check empty condition
print("Stack Underflow....")
else:
self.Stack.pop(). # delete item from top of stack using pop method
self.top -= 1 # decrement top by 1
def peep(self): #peep method
print(self.top,"\t",self.Stack[-1]) #display top item
def disp (self): # display method
if self.top == -1: # check empty condition
print("Stack Underflow....")
else:
print("TOP \tELEMENT")
for i in range(self.top,-1,-1): # print items and top
print(i," \t",self.Stack[i])
n = int(input("Enter Size :: ")) # size of stack
stk = stack(n) # object and pass n as size
while(True): # loop for choice as a switch case
print(" 1: PUSH ")
print(" 2: POP ")
print(" 3: PEEP ")
print(" 4: PRINT ")
print(" 5: EXIT ")
option = int(input("enter your choice :: "))
if option == 1:
stk.push()
elif option == 2:
stk.pop()
elif option == 3:
stk.peep()
elif option == 4:
stk.disp()
elif option == 5:
print("you are exit!!!!!")
break
else:
print("Incorrect option")