class Stack:
def __init__(
self):
self.items = []
def isEmpty(
self):
return self.items == []
def push(
self, item):
self.items.append(item)
def pop(
self):
return self.items.pop()
def peek(
self):
return self.items[
len(
self.items)-
1]
def size(
self):
return len(
self.items)
def infixToPostfix(infixexpr):
'''
中缀转后缀
:param infixexpr:
:return:
'''
prec = {}
prec[
'*'] =
3
prec[
'/'] =
3
prec[
'+'] =
2
prec[
'-'] =
2
prec[
'('] =
1
opStack = Stack()
postfixList = []
# tokenList = infixexpr.split()
# print(tokenList)
for token
in infixexpr:
if token
in '0123456789':
postfixList.append(token)
elif token ==
'(':
opStack.push(token)
elif token ==
')':
topToken = opStack.pop()
while topToken !=
'(':
postfixList.append(topToken)
topToken = opStack.pop()
else:
while (
not opStack.isEmpty())
and \
(prec[opStack.peek()] >= prec[token]):
print(opStack)
postfixList.append(opStack.pop())
opStack.push(token)
while not opStack.isEmpty():
postfixList.append(opStack.pop())
return ''.join(postfixList)
def postfixEval(postfixExpr):
operandStack = Stack()
# tokenList = postfixExpr.split()
for token
in postfixExpr:
if token
in '0123456789':
operandStack.push(
int(token))
else:
operand2 = operandStack.pop()
operand1 = operandStack.pop()
result = doMath(token
, operand1
, operand2)
operandStack.push(result)
return operandStack.pop()
def doMath(op
, op1
, op2):
if op ==
'*':
return op1 * op2
elif op ==
'/':
return op1 / op2
elif op ==
'+':
return op1 + op2
else:
return op1 - op2
