如何更正括号的添加，以免不必要地使用括号 python3.

Question

我正在制作一个将前缀转换为中缀的程序，并且在将括号放入表达式时遇到问题。 对于转换，我使用经典的堆栈算法。这是我对肮水菜的函数。

1. 输入：

   //+86 16 67/*/31 53 85 15 
   

2. 我的输出：

   ((86+16)/67)/(((31/53)*85)/15)
   

3. 预期输出：

   (86+16)/67/(31/53*85/15)
   

def breckets(operand1, operand2, operace):
res = ""
if (operand1.isdigit()) and (operand2.isdigit()):
res = operand1 + operace + operand2
elif (operand1.isdigit()) and (not operand2.isdigit()):
if operace == "+":
res = operand1 + operace + operand2
else:
res = operand1 + operace + "(" + operand2 + ")"
elif (not operand1.isdigit()) and (operand2.isdigit()):
if prior(operace) != 0:
res = "(" + operand1 + ")" + operace + operand2
else:
res = operand1 + operace + operand2
else:
res = "(" + operand1 + ")" + operace + "(" + operand2 + ")"
return res

def prior(a):
prior = None
if a in "+-":
prior = 0
elif a in "*/":
prior = 1
elif a in "^":
prior = 2
else:
print("Something went wrong")
exit()
return prior

但是我不能不必要地使用括号，有人可以给我一些建议吗？

Answer 1

下面的代码可以得到你期望的。 但我不确定算法是否正确，因为我不熟悉数据结构。

我使用基本函数对列表进行多次排序，而不是严格从右到左对列表进行排序，您可以更改一些行来打破 while 循环以使其如此，如果这是您想要的。

无论如何，希望这可以以某种方式帮助您。

operators = "+-*/^"
# presume the input is a finely spaced str that can be splitted into a proper list
# ipt = "/ * + 86 16 67 / * / + 31 53 85 15 / / 33 45 74"  # for testing
ipt = "/ / + 86 16 67 / * / 31 53 85 15"  
ip = ipt.split()

def sorting(lst):
res = []
i = len(lst)-1  # check list items from right to left
while i >= 0:
if i >= 3:
if lst[i-2] in operators:
# check if the operator is followed by two numbers
if lst[i-1] not in operators and lst[i] not in operators: 
# check if the operator is + | -, the result should be in parentheses
if lst[i-2] in "+-":
res.append("(" + lst[i-1] + lst[i-2] + lst[i] + ")")
i -=3
continue
# if the operator is following another operator, the result shouldn't be in parentheses
if lst[i-3] in operators:
res.append(lst[i-1] + lst[i-2] + lst[i])
i -=3
continue
# if the operator is following a number, the result shouldn be in parentheses
else:
res.append("(" + lst[i-1] + lst[i-2] + lst[i] + ")")
i -= 3
continue
# this is to check the first item of the list is an operator and followed by two numbers
elif i == 2:
if lst[i-2] in operators:
if lst[i-1] not in operators and lst[i] not in operators:
res.append(lst[i-1] + lst[i-2] + lst[i])
i -=3
continue
res.append(lst[i])
i -= 1
# as all items are appending to the new list, so the positions are totally reversed
return list(reversed(res))
def no_more_operators(lst):
# to check if the lst is sortable
# one scenario is there are exccesive numbers, but no operators
# the current function can only check if any operators is in the list
for op in operators:
if op in lst:
return False
return True
def no_more_numbers(lst):
# to check if the lst is sortable
# one scenario is there are exccesive operators, but no numbers
# the current function can only check if any number is in the list
for i in lst:
if i.isnumeric():
return False
return True
# keep sorting the list until there is no more numbers or n0 more operators
while not no_more_numbers(ip) or not no_more_operators(ip):
ip = sorting(ip)
print(ip)

输出：

['/', '/', '(86+16)', '67', '/', '*', '31/53', '85', '15']
['/', '(86+16)/67', '/', '31/53*85', '15']
['/', '(86+16)/67', '(31/53*85/15)']
['(86+16)/67/(31/53*85/15)']