class MyQueue(object):
def __init__(self, capacity):
self.output_stack = MyStack(capacity)
self.help_stack = MyStack(capacity)
self.capacity = capacity
self.current_capacity = capacity
def __str__(self):
output = "Queue: " + str(self.output_stack) + "\n"
output += "Helper: " + str(self.help_stack)
return output
def add(self, value):
if self.current_capacity > 0:
if self.output_stack.is_empty() == True:
self.output_stack.push(value)
else:
while self.output_stack.is_empty() == False:
self.help_stack.push(self.output_stack.pop())
self.output_stack.push(value)
self.current_capacity -= 1
while self.help_stack.is_empty() == False:
self.output_stack.push(self.help_stack.pop())
else:
raise QueueOverFlow
def remove(self):
try:
return self.output_stack.pop()
except:
raise EmptyQueueExeption
def infix_to_prefix(infix):
"""Converts given infix expression to postfix expression
using Shunting Yard Algorithm and converts that postfix to prefix"""
if infix == "":
return ""
#stack to temporarily store operators and paranthesis
stack = MyStack(size=len(infix) + 1)
postfix = [] # a list to store postifix expression
for char in infix:
if is_operand(char):
postfix.append(char)
elif char not in ['(', ')']:
while not stack.is_empty() and precedence(char) <= precedence(
stack.top()):
#Add elements from stack until stack is not empty and precedence of \n
#char is less than the top most stack element
postfix.append(stack.pop())
stack.push(char)
elif char == "(":
stack.push(char)
elif char == ")":
while not stack.is_empty() and stack.top() != "(":
postfix.append(stack.pop())
if stack.top() != "(":
raise ValueError("Parathesis Mismatch!")
stack.pop()
while not stack.is_empty():
# pop out and add all existing elements from stack and add in onto postfix
postfix.append(stack.pop())
stack.clear_stack()
# returns prefix string after converting the postfix passed to convert_to_prefix
return convert_to_prefix(postfix)
def dequeue(self):
# Write your code here
temp_stack = MyStack()
while not self.main_stack.size() == 1:
temp_stack.push(self.main_stack.pop())
popped_item = self.main_stack.pop()
while not temp_stack.is_empty():
self.main_stack.push(temp_stack.pop())
return popped_item
def infix_to_postfix(infix):
"""Converts given infix expression to postfix expression
using Shunting Yard Algorithm"""
#stack to temporarily store operators and paranthesis
stack = MyStack(size= len(infix)+1)
postfix = [] # a list to store postifix expression
# Returns True if char is an operand
is_operand = lambda char: char.isalpha() or char.isnumeric()
# Returns the precedence of char from PRIORITY dict"""
PRIORITY = {"+": 1, "-": 1, "*": 2, "/": 2, "%": 2, "^": 3}
precedence = lambda char: PRIORITY[char] if char in PRIORITY else -1
for char in infix:
if is_operand(char):
postfix.append(char)
elif char not in ['(',')']:
while not stack.is_empty() and precedence(char) <= precedence(stack.top()):
#Add elements from stack until stack is not empty and precedence of \n
#char is less than the top most stack element
postfix.append(stack.pop())
stack.push(char)
elif char == "(":
stack.push(char)
elif char == ")":
while not stack.is_empty() and stack.top() != "(":
postfix.append(stack.pop())
if stack.top() != "(":
raise ValueError("Parathesis Mismatch!")
stack.pop()
while not stack.is_empty():
# pop out and add all existing elements from stack and add in onto postfix
postfix.append(stack.pop())
return " ".join(postfix)
