def conversionToPostOrder(self, inOrdErexpr):
"""
后序转换
"""
# 构建运算符优先级字典
prec = {"*": 3, "/": 3, "+": 2, "-": 2, "(": 1, ")": 1}
if not self.parseChecker(inOrdErexpr):
raise ValueError
opStack = Stack()
postOrderList = list()
exprList = inOrdErexpr.split()
for ch in exprList:
if ch.isdigit():
postOrderList.append(ch)
elif ch == "(":
opStack.push(ch)
elif ch == ")":
topOper = opStack.pop()
while topOper != "(":
postOrderList.append(topOper)
topOper = opStack.pop()
else:
# 比较运算符优先级，如果栈中运算符的优先级>当前运算符， 追加至转换列表中
while (not opStack.isEmpty()) and (prec[opStack.peek()] >
prec[ch]):
postOrderList.append(opStack.pop())
opStack.push(ch)
# 将栈中的运算符追加至转换列表中
while not opStack.isEmpty():
postOrderList.append(opStack.pop())
return "".join(postOrderList)
class MyQueue:
def __init__(self):
self.new_stack = Stack()
self.old_stack = Stack()
def _shift_stacks(self):
if self.old_stack.is_empty():
while not self.new_stack.is_empty():
self.old_stack.push(self.new_stack.pop())
def add(self, value):
return self.new_stack.push(value)
def peek(self):
if self.is_empty():
return False
self._shift_stacks()
return self.old_stack.peek()
def remove(self):
if self.is_empty():
return False
self._shift_stacks()
return self.old_stack.pop()
def is_empty(self):
return len(self) == 0
def __len__(self):
return len(self.new_stack) + len(self.old_stack)
class MinStack(Stack):
def __init__(self):
super().__init__()
self.minvals = Stack()
def push(self, value):
super().push(value)
if not self.minvals or value <= self.min():
self.minvals.push(value)
def pop(self):
value = super().pop()
if value == self.min():
self.minvals.pop()
return value
def min(self):
return self.minvals.peek()