def balance_parens(infix_string):
valid_ops = ["+", "-", "*", "/"]
opstack = Stack()
output = list()
infix_string = infix_string.split()
for char in infix_string:
if char == "(":
opstack.push(char)
elif char == ")":
opstack.pop()
elif char in valid_ops:
opstack.append(char)
return output
def calculator(str):
expression = [] #list
numbers = []
operator = Stack() #stack
ranking = {'+': 1, '-': 1, '*': 2, '/': 2}
middle_num = 0
right_num = 0
left_num = 0
# 담기
#숫자 : 배열에 넣기
#기호(맨 위 연산자보다 우선순위가 낮거나 같을 때 ) : 기존 값들을 배열에, 본인은 스택에
#기호(우선순위 높을 때) : 스택에 본인 값 저장
for s in str:
if s.isdigit():
expression.append(s)
elif s in ranking.keys():
if len(operator) == 0:
operator.append(s)
elif ranking[s] <= ranking[operator.peek()]:
while operator:
expression.append(operator.pop())
operator.push(s)
else:
operator.push(s)
# 남은 기호들 배열에 넣기
while operator:
expression.append(operator.pop())
# 계산하기
for e in expression:
if e.isdigit():
numbers.push(e)
else:
right_num = int(numbers.pop())
left_num = int(numbers.pop())
if e == '+':
middle_num = left_num + right_num
elif e == '-':
middle_num = left_num - right_num
elif e == '*':
middle_num = left_num * right_num
elif e == '/':
middle_num = left_num / right_num
numbers.push(middle_num)
return numbers.pop()
