数据结构（3）队列及栈实现后缀表达式 01/28

队列

#普通队列
class myQuene(object):
    def __init__(self,list=[]):
        self.__list = list
    def size(self):
        return len(self.__list)
    def __delete__(self):
        if self.size == 0:
            print("空队列不能删除")
        else:
            temp_delete = self.__list[0]
            del self.__list[0]
            return  temp_delete
    def insert(self,data):
        self.__list.append(data)
    def peek(self):
        if self.size == 0:
            print("空队列不能删除")
        else:
            return self.__list[0]

#优先级队列
class myPQuene(object):
    def __init__(self,list=[]):
        self.__list = list
    def size(self):
        return len(self.__list)
    def __delete__(self):
        if self.size == 0:
            print("空队列不能删除")
        else:
            temp_delete = self.__list[0]
            del self.__list[0]
            return  temp_delete
    def insert(self,data):
        if self.size == 0:
            self.__list.append(data)#若队列为空，将数据直接插入
        else:
            temp = -1
            for i in range(len(self.__list)):
                if self.__list[1] > data:
                    temp = i
                    break
            if temp == -1:
                self.__list.append(data)
            else:
                self.__list.insert(temp,data)

    def peek(self):
        if self.size == 0:
            print("空队列不能查看")
        else:
            return self.__list[0]

#循环队列
class cycle():
    def __init__(self,list=[],first=None,last=None):
        self.__list = list
        self.__last = last
        self.__first = first
    def size(self):
        length = 0
        if self.__last > self.__first:
            length = self.__last - self.__first + 1
        elif self.__last == self.__first and self.__last != None:
            length = 1
        elif self.__last == self.__first and self.__last == None:
            length = 0
        else:
            length = len(self.__list) - (self.__first - self.__last - 1)
            return length
    def insert(self,data):
        if self.size == 0:
            self.__list.append(data)
            self.__first = 0
            self.__last = 0
        else:
            if self.size() == len(self.__list):
                self.insert(self.__last+1,data)
                self.__last = self.__last+1
            else:
                if self.__last+1 == len(self.__list):
                    self.__list[0] = data
                    self.__last = 0
                else:
                    self.__list[self.__last+1] = data
                    self.__last = self.__last+1
    def delete(self):
        if self.size == 0:
            print("空队列，无法删除")
        elif self.size() == 1:
            temp = self.__first
            self.__first = None
            self.__last = None
            return temp
        else:
            temp = self.__list[self.__first]
            if self.__first+1 == len(self.__list):
                self.__first = 0
            else:
                self.__first = self.__first+1
            return temp
    def peek(self):
        if self.size == 0:
            print("空队列，无法查看")
        else:
            return self.__list[self.__first]

前，中，后缀表达式转换

步骤：
1，中缀表达式转后缀表达式
1）遇到操作数直接拼到字符串
2）遇到操作符
a,遇到左括号
b,遇到右括号
c,遇到加减
d,遇到乘除
2，计算后缀表达式

#中缀表达式转后缀表达式
def middle2after(s=""):
    rule = {"-":1,"+":1,"*":2,"/":2}
    str = ""
    list = []
    for item in s:
        if item.isalnum():
            str += item
        else:
            if item == "(":
                list.append(item)
            elif item == ")":
                while list[-1] != "(":
                    str += list.pop()
                list.pop()
            elif item in "+-":
                if len(list) == 0:
                    list.append(item)
                else:
                    while len(list) != 0 and list[-1] != "(":
                        str += list.pop()
                    list.append(item)
            elif item in "*/":
                list.append(item)
            else:
                print("表达式有问题")
    while len(list) != 0:
        str += list.pop()
    return str

#后缀表达式
def cal(s=""):
    stack = []
    for item in s:
        if item.isalnum():
            stack.append(item)
        else:
            a = float(stack.pop())
            b = float(stack.pop())
            if item == "-":
                c = b - a
            elif item == "+":
                c = b + a
            elif item == "*":
                c = b * a
            elif item == "/":
                c = b / a
            else:
                print("后缀表达式有问题")
            stack.append(c)
    return stack.pop()