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creating mergeable stack

class Node():

def __init__(self,data):

self.next = None

self.prev = None

self.data = data

class Stack():

def __init__(self):

self.head = None

self.tail = None

def push(self, data):

new_node = Node(data)

if (self.head == None):

self.head = new_node

self.head.next= None

self.head.prev = None

self.tail = new_node

else:

new_node.prev = self.tail

self.tail.next = new_node

self.tail = new_node

def pop(self):

if (self.head == None):

print("Stack underflow")

if (self.head == self.tail):

self.head = None

self.tail = None

else:

node = self.tail

self.tail = self.tail.prev

del node

self.tail.next = None

def merge(self, stack):

if stack.head == None: return 

if self.head == None:

self.head = stack.head

self.tail = stack.tail

return

self.head.prev = stack.tail 

stack.tail.nxt = self.head

self.head = stack.head

def display(self):

if (self.tail != None):

n = self.tail

while (n != None):

print(n.data, end = " ")

n = n.prev

print()

else:

print("Stack Underflow")

ms1 = Stack()

ms2 = Stack()

ms1.push(6)

ms1.push(5)

ms1.push(4)

ms2.push(9)

ms2.push(8)

ms2.push(7)

ms1.merge(ms2)

ms1.display()

while ms1.head != ms1.tail:

ms1.pop ()

print ("check pop all elements until head == tail (one element left)")

print ("on merged stack: ", end = "")

ms1.display()

Find all triplets with zero sum

def triplets(arr, n):

f = False

for i in range(0, n-2):

for j in range(i+1, n-1):

for k in range(j+1, n):

if (arr[i] + arr[j] + arr[k] == 0):

print(arr[i], arr[j], arr[k])

f = True

if (f == False):

print(" not exist ")

arr = [0, -1, 2, -3, 1]

n = len(arr)

triplets(arr, n)

Interleave the first half of the queue with second half

from queue import Queue

def interLeaveQueue(q):

if (q.qsize() % 2 != 0):

print("Input even number of integers.")

s = []

size = int(q.qsize() / 2)

for i in range(size):

s.append(q.queue[0])

q.get()

while len(s) != 0:

q.put(s[-1])

s.pop()

for i in range(size):

q.put(q.queue[0])

q.get()

for i in range(size):

s.append(q.queue[0])

q.get()

while len(s) != 0:

q.put(s[-1])

s.pop()

q.put(q.queue[0])

q.get()

if __name__ == '__main__':

q = Queue()

q.put(11)

q.put(12)

q.put(13)

q.put(14)

q.put(15)

q.put(16)

q.put(17)

q.put(18)

q.put(19)

q.put(20)

interLeaveQueue(q)

length = q.qsize()

for i in range(length):

print(q.queue[0], end=" ")

q.get()

Find size of Doubly Linked List

class Nodes:

def __init__(self):

self.data = None

self.next = None

self.prev = None

def push( ref, new_data):

new_node = Nodes()

new_node.data = new_data

new_node.next = (ref)

new_node.prev = None

if ((ref) != None):

(ref).prev = new_node

(ref) = new_node

return ref

def findSize(node):

res = 0

while (node != None):

res = res + 1

node = node.next

return res

head = None

head = push(head, 4)

head = push(head, 3)

head = push(head, 2)

head = push(head, 1)

print(findSize(head))