def infix_2_postfix(infix_expr):
postfix = "" # empty string where operands operators and popped items from stack will go
operator_stack = Stack() # Empty stack to push items
for symbol in infix_expr:
if symbol == " " or symbol == '\t': # Ignore white spaces
continue
if symbol == '(':
operator_stack.push(symbol)
elif symbol == ')':
top_symbol_stack = operator_stack.pop()
while top_symbol_stack != '(':
postfix += top_symbol_stack
top_symbol_stack = operator_stack.pop()
elif symbol in '+-*/%^':
while not operator_stack.is_empty() and precedence(
operator_stack.peek()) >= precedence(symbol):
# If the precedence in the stack is >= scanned symbol pop from stack and add to postfix list
postfix += operator_stack.pop()
operator_stack.push(
symbol) # When finished push the scanned symbol
else: # Its an operand add it to postfix string
postfix += symbol
while not operator_stack.is_empty():
postfix += operator_stack.pop()
return postfix
def divide_by_two(number):
remainder_stack = Stack() # Create an empty stack
while number > 0:
remainder = number % 2
remainder_stack.push(remainder)
number = number // 2
# remainder_stack.display() Prints the stack in list form
result = ''
while not remainder_stack.is_empty():
result = result + str(remainder_stack.pop())
return result
def base_conversion(number, base):
digits = '0123456789ABCDEF'
remainder_stack = Stack()
while number > 0:
remainder = number % base
remainder_stack.push(remainder)
number = number // base
result = ''
while not remainder_stack.is_empty():
result = result + str(digits[remainder_stack.pop()])
return result
def postfix_eval(postfix_expr):
operand_stack = Stack()
tokenList = postfix_expr.split()
for token in tokenList:
if token in '0123456789':
operand_stack.push(int(token))
else:
operand2 = operand_stack.pop(
) # The last number popped is the second operand
operand1 = operand_stack.pop()
result = do_math(token, operand1, operand2)
operand_stack.push(result)
return operand_stack.pop()
def par_checker(symbol_strng):
s = Stack() # Empty stack to place parentheses
balanced = True
index = 0
while index < len(symbol_strng) and balanced:
symbol = symbol_strng[index] # First parentheses is at index 0
if symbol in "([{":
s.push(symbol)
else:
if s.is_empty():
balanced = False
else:
top_open = s.pop()
if not matches(top_open, symbol):
balanced = False
index += 1
return balanced and s.is_empty()
def is_valid(expression):
# Create an empty stack
par_stack = Stack()
for ch in expression:
if ch in '({[':
par_stack.push(ch)
if ch in ')}]':
if par_stack.is_empty():
print("Right parentheses are more then left parentheses.")
return False
else:
popped_char = par_stack.pop()
if not matched_parentheses(popped_char, ch):
print("Mismatched parentheses are ", popped_char, " and ", ch)
return False
if par_stack.is_empty():
print("Balanced parentheses")
return True
else:
print("Left parentheses are more than right parentheses")
return False
def infix_to_postfix(infix_expr):
# Prec holds the precedence
prec = {}
prec['**'] = 4
prec['*'] = 3
prec['/'] = 3
prec['+'] = 2
prec['-'] = 2
prec['('] = 1
operator_stack = Stack() # Empty stack for the operators
postfixList = [] # Empty stack for the post fix list
tokenList = infix_expr.split() # Lets split the expression
# Lets read each token
for token in tokenList:
if token in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' or token in '0123456789':
# Append token to the postfixList
postfixList.append(token)
elif token == '(':
# Push the token to operator stack
operator_stack.push(token)
elif token == ')':
# pop last item from operator stack
topToken = operator_stack.pop()
while topToken != '(':
postfixList.append(topToken)
topToken = operator_stack.pop()
else:
while (not operator_stack.is_empty()) and (
prec[operator_stack.peek()] >= prec[token]):
postfixList.append(operator_stack.pop())
operator_stack.push(token)
while not operator_stack.is_empty():
postfixList.append(operator_stack.pop())
return " ".join(postfixList)
from Stack1 import Stack
s = Stack()
print s.isEmpty()
s.push("s")
print s.size()
s.push("apple")
print s.isEmpty()
s.push("big")
print s.pop()
print s.pop()
print s.size()
print s.pop()
s.pop()
def postfix_evaluation(postfix_expr):
# Create an empty stack
st = Stack()
# Traverse the expression
for symbol in postfix_expr:
if symbol.isdigit():
st.push(int(symbol))
else:
x = st.pop()
y = st.pop()
if symbol == '+':
st.push(y + x)
elif symbol == '-':
st.push(y - x)
elif symbol == '*':
st.push(y * x)
elif symbol == '/':
st.push(y / x)
elif symbol == '%':
st.push(y % x)
elif symbol == '^':
st.push(y**x)
return st.pop()