class Calculator():
def __init__(self):
self.operators = Stack()
self.operands = Stack()
self.operatorsMap = {'/': 2, '*': 2, '-': 1, '+': 1, '(': 0, ')': 0}
def evaluate(self, expression):
if expression is None or len(expression) == 0:
return 0
expression = expression.split(' ')
for ch in expression:
if self.isOperand(ch):
self.operands.push(int(ch))
elif ch == '(':
self.operators.push(ch)
elif ch == ')':
while self.operators.peek() != '(':
self.process()
self.operators.pop()
elif self.isOperator(ch):
while not self.operators.empty() and self.precedence(
self.operators.peek()) >= self.precedence(ch):
self.process()
self.operators.push(ch)
while not self.operators.empty():
self.process()
return self.operands.pop()
def process(self):
map = {'+': self.add, '-': self.sub, '*': self.multi, '/': self.divide}
right = self.operands.pop()
left = self.operands.pop()
operator = self.operators.pop()
func = map[operator]
r = func(left, right)
self.operands.push(r)
def isOperand(self, char):
return re.match(r'^\d+$', char) is not None
def isOperator(self, char):
return char in self.operatorsMap
def precedence(self, operator):
if operator not in self.operatorsMap:
raise Exception(f"unknown operateor {operator}")
return self.operatorsMap[operator]
def add(self, left, right):
return left + right
def sub(self, left, right):
return left - right
def divide(self, left, right):
return left / right
def multi(self, left, right):
return left * right
