def infix_to_postfix(infix):
"""
中缀转后缀
:param infix:中缀表达式
:return: 后缀表达式
"""
opstack = Stack() # 操作符栈
result = []
for token in infix:
if is_operand(token): # 操作数
result.append(token)
elif token == '(': # 遇到左括号，入栈
opstack.push(token)
elif token == ')': # 遇到右括号，弹栈并将值放至result列表末尾, 直到遇到左括号
_token = opstack.pop()
while _token and _token != '(':
result.append(_token)
_token = opstack.pop()
else: # 遇到操作符，压栈，但是如果在栈中有比当前操作符优先级高的任何操作符要先弹出
while not opstack.is_empty():
top_token = opstack.peek()
if higher_precedence(top_token, token):
result.append(opstack.pop())
else:
break
opstack.push(token)
while not opstack.is_empty():
result.append(opstack.pop())
return ''.join(result)
def brackets_match(bracket_str):
"""括号匹配"""
balanced = True
stack = Stack()
for s in bracket_str:
if s == '(':
stack.push(s)
else:
if stack.is_empty():
balanced = False
break
else:
stack.pop()
return balanced and stack.is_empty()
def symbol_match(symbol_str):
balanced = True
stack = Stack()
for s in symbol_str:
if s in OPEN_CHARS:
stack.push(s)
else:
if stack.is_empty():
balanced = False
break
else:
top_val = stack.pop()
if not match(top_val, s):
balanced = False
break
return balanced and stack.is_empty()
def convert_to_binary(number):
s = Stack()
while number:
s.push(number % 2)
number /= 2
bin_digits = []
while not s.is_empty():
bin_digits.append(str(s.pop()))
return ''.join(bin_digits)
def test_is_empty_with_empty(self):
mystack = Stack()
self.assertTrue(mystack.is_empty())