class BalancedParentheses:
def __init__(self):
self.myStack = Stack(100)
def AreParanthesesBalanced(self, expression):
for c in expression:
if (c == '[' or c == '{' or c == '('):
self.myStack.push(c)
if (c == ']' or c == '}' or c == ')'):
if (self.myStack.isEmpty()
or not self.ArePair(self.myStack.topElement(), c)):
return False
else:
self.myStack.pop()
if (self.myStack.isEmpty()):
return True
else:
return False
def ArePair(self, opening, closing):
if (opening == '[' and closing == ']'):
return True
elif (opening == '{' and closing == '}'):
return True
elif (opening == '(' and closing == ')'):
return True
else:
return False
class PrefixEvaluation:
def __init__(self):
self.myStack = Stack(100) # define stack of 100 elements
def evaluatePrefix(self, expression):
for c in reversed(expression):
if (self.isOperand(c)):
self.myStack.push(c)
elif (self.isOperator(c)):
oprand1 = self.myStack.pop()
oprand2 = self.myStack.pop()
result = self.performOperation(c, oprand1, oprand2)
self.myStack.push(result)
else:
print("error!!!")
return self.myStack.topElement()
def isOperand(self, c):
if (c >= '0' and c <= '9'):
return True
else:
return False
def isOperator(self, c):
if (c == '+' or c == '-' or c == '*' or c == '/'):
return True
else:
return False
def performOperation(self, operator, oprand1, oprand2):
if (operator == '+'):
return int(oprand1) + int(oprand2)
elif (operator == '-'):
return int(oprand1) - int(oprand2)
elif (operator == '*'):
return int(oprand1) * int(oprand2)
elif (operator == '/'):
return int(oprand1) / int(oprand2)
else:
print("error!!!")
def test_topElement_stackEmpty(self):
myStack = Stack(10)
self.assertEqual(myStack.topElement(), "Stack empty")
def test_topElement(self):
myStack = Stack(10)
myStack.push(10)
self.assertEqual(myStack.topElement(), 10)