05案例-逆波兰计算器.ipynb

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    "林肯：  https://www.bilibili.com/video/BV1Hd4y1B7Mg?p=15&spm_id_from=pageDriver&vd_source=e1de9f6d02128b9c85f5fdd03c7e72fc\n"
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    "#-----------------------------逆波兰计算器--------------------------------\n",
    "class Stack():#定义一个栈\n",
    "    def __init__(self,):\n",
    "        self.stack = []\n",
    "    def push(self,data):#入栈\n",
    "        self.stack.append(data)\n",
    "    def pop(self):#出栈\n",
    "        return self.stack.pop()\n",
    "    def is_empty(self):#是否栈空\n",
    "        return not len(self.stack)\n",
    "    def top(self):#栈顶元素\n",
    "        if self.is_empty():\n",
    "            return None\n",
    "        return self.stack[-1]\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "\n",
    "\n"
   ]
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   "cell_type": "code",
   "execution_count": 40,
   "metadata": {},
   "outputs": [],
   "source": [
    "#逆波兰计算器\n",
    "class InversPolishCalculator(object):\n",
    "\n",
    "    #主程序,传入中缀表达式,返回结果\n",
    "    def deal(self,exspression):\n",
    "        list_expression = self.get_list_expression(exspression)\n",
    "        stack = Stack()  # 实例化栈\n",
    "        for ele in list_expression:  # 处理逆波兰表达式\n",
    "            if ele.replace('.','').isdigit():  # 是数字压入栈\n",
    "                stack.push(ele)\n",
    "            else:  \n",
    "                # 是运算符进行运算,用次顶元素,和栈顶元素\n",
    "                ret = self.operation(ele, float(stack.pop()), float(stack.pop()))\n",
    "                stack.push(ret)\n",
    "        return '%.2f'% stack.pop()#返回结果\n",
    "\n",
    "    # 定义算法\n",
    "    def operation(self,sign, num2, num1):  \n",
    "        if sign == '*':\n",
    "            return num1 * num2\n",
    "        if sign == '/':\n",
    "\n",
    "            return num1/num2\n",
    "        if sign == '+':\n",
    "            return num1 + num2\n",
    "        if sign == '-':\n",
    "            return num1 - num2\n",
    "\n",
    "    # 处理中缀表达式字符串,转为列表形式方便计算\n",
    "    def deal_str(self,exspression):\n",
    "        status = 0\n",
    "        res = ''\n",
    "        exspression = exspression.strip().replace(' ','')\n",
    "        for ele in exspression:\n",
    "            if ele.isdigit() or ele =='.':\n",
    "\n",
    "                # 如果前面是数字\n",
    "                if status == 1:\n",
    "                    res =res.strip(' ')\n",
    "                    res = res + ele + ' '\n",
    "\n",
    "                # 说前面数字不是连着的\n",
    "                else:\n",
    "                    status = 1\n",
    "                    res= res+ele+' '\n",
    "            else:\n",
    "                # 如果是符号\n",
    "                status = 0\n",
    "                res = res + ele + ' '\n",
    "\n",
    "        return res.strip().split(' ') # 将字符都分开 一个一个的输出\n",
    "\n",
    "\n",
    "    #将中缀表达式列表形式转后缀\n",
    "    def get_list_expression(self,exspression):\n",
    "        lst = self.deal_str(exspression)   # lst ---》['1', '+', '(', '(', '2', '+', '3', ')', '*', '4', ')', '-', '5']\n",
    "        s1 = Stack()   # 实例化的时候主要是用到__init__函数\n",
    "        s2 = Stack()\n",
    "        for ele in lst:\n",
    "            if ele.replace('.','').isdigit():\n",
    "                s2.push(ele)   # 数字的话就进栈\n",
    "            else:\n",
    "                self.deal_symbol(ele,s1,s2) # \n",
    "        while not s1.is_empty():\n",
    "            s2.push(s1.pop())\n",
    "        res = []\n",
    "        while not s2.is_empty():\n",
    "            res.append(s2.pop())\n",
    "        return res[::-1]\n",
    "\n",
    "    def deal_symbol(self,ele,s1,s2): # 处理符号入栈出栈问题\n",
    "        if s1.is_empty() or s1.top() == '(' or ele == '(':  # 是空的  第一个  s1.top() 栈顶元素\n",
    "            s1.push(ele)\n",
    "        elif ele == ')':\n",
    "            while s1.top() != '(':  # s1不是（， 把符号压入数字那一端\n",
    "                s2.push(s1.pop())\n",
    "            s1.pop()\n",
    "        elif self.get_priority(ele) > self.get_priority(s1.top()):\n",
    "            s1.push(ele)\n",
    "        else:\n",
    "            s2.push(s1.pop())\n",
    "            self.deal_symbol(ele,s1,s2)\n",
    "\n",
    "    def get_priority(self,sign):#获取符号优先级\n",
    "        if sign=='*' or sign=='/':\n",
    "            return 2\n",
    "        elif sign=='+' or sign=='-':\n",
    "            return 1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 41,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "计算结果: 16.00\n"
     ]
    }
   ],
   "source": [
    "if __name__ == '__main__':\n",
    "    # exspression = input('请输入计算公式:')\n",
    "    exspression = \"1+((2+3)*4)-5\"\n",
    "    Calculator = InversPolishCalculator()\n",
    "    ret = Calculator.deal(exspression)\n",
    "    print('计算结果:',ret)\n",
    "    # input()"
   ]
  }
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