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 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)
