def is_balanced(brackets):
brackets = brackets.strip()
if brackets == '':
raise Exception("The string is empty")
if '(' not in brackets and ')' not in brackets:
raise Exception("This string without brackets")
stack = Stack()
for bracket in brackets:
if bracket == ')' and stack.is_empty():
print(
"The string is started with closed bracket and it is not balanced"
)
return False
elif bracket == '(':
stack.push(bracket)
elif bracket == ')':
stack.pop()
else:
raise Exception("This string has something else but brackets")
if stack.is_empty():
print("The string is balanced")
return True
else:
print("The string is not balanced")
return False
def calculate_postfix(expression):
S = Stack()
if not expression:
raise Exception("The string is empty")
for item in expression:
if item.isdigit():
S.push(int(item))
elif item == "+":
val1 = S.pop()
val2 = S.pop()
S.push(val1 + val2)
elif item == "*":
val1 = S.pop()
val2 = S.pop()
S.push(val1 * val2)
elif item == "-":
val1 = S.pop()
val2 = S.pop()
S.push(val1 - val2)
elif item == "/":
val1 = S.pop()
val2 = S.pop()
S.push(val1 / val2)
elif item == "=":
return S.pop()
return S.pop()
def test_pop_one_element(self):
stack = Stack()
stack.push(1)
stack.pop()
self.assertEqual(stack.tail, None)
self.assertEqual(stack.head, None)
self.assertEqual(stack.size(), 0)
def test_pop_two_element(self):
stack = Stack()
stack.push(1)
stack.push(2)
self.assertEqual(stack.pop(), 2, "We should pop 2")
self.assertEqual(stack.peek(), 1)
self.assertEqual(stack.size(), 1)
self.assertEqual(stack.pop(), 1, "We should pop 1")
self.assertEqual(stack.size(), 0)
def test_stack_peek(self):
stack = Stack()
stack.push(77)
stack.push(123)
self.assertEqual(stack.peek(), 123, "We should peek 123")
self.assertEqual(stack.pop(), 123, "We hsould pop 123")
self.assertEqual(stack.peek(), 77, "We should peek 77")
self.assertEqual(stack.pop(), 77, "We should pop 77")
self.assertEqual(stack.size(), 0)
self.assertIsNone(stack.peek(), "peek is none")
def addTail(self, item):
Stack.push(self,item)
def enqueue(self, item): #need to add element to the end of the list
Stack.push(self, item)