简易计算器-leetcode
今天，开始在leetcode上面开始做题，第一个题目是：
Implement a basic calculator to evaluate a simple expression string.
The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.
You may assume that the given expression is always valid.
Some examples:
"3+2*2" = 7
" 3/2 " = 1
" 3+5 / 2 " = 5
主要思想，先将中缀表达式利用“栈”和“队列”，转换为后缀表达式，其实难点也主要在这里，再计算后缀表达式的值。
首先构造“栈”：
stack.py
class Stack():
def __init__(self, size):
self.size = size
self.top = -1
self.stack = []
def push(self, ele):
if self.isfull():
raise Exception("out of range")
else:
self.stack.append(ele)
self.top += 1
def isfull(self):
if self.top == self.size - 1:
return True
else:
return False
def pop(self):
if self.isEmpty():
raise Exception("no element")
else:
self.top -= 1
return self.stack.pop()
def isEmpty(self):
if self.top == -1:
return True
else:
return False
def returnFristEle(self):
return self.stack[self.top]
def returnStack(self):
return self.stack
if __name__ == '__main__':
s = Stack(1)
for i in xrange(3):
s.push(i)
print s.stack, s.top
接下来，需要构造“队列”：
__author__ = 'Administrator'
class Queue():
def __init__(self, size):
self.size = size
self.queue = []
self.top = -1
def push(self, ele):
if not self.isFull():
self.queue.append(ele)
self.top += 1
else:
raise Exception("out of range")
def isFull(self):
if self.top == self.size - 1:
return True
else:
return False
def isEmpty(self):
if self.size == self.top:
return True
else:
return False
def pop(self):
if self.isEmpty():
raise Exception("no element")
else:
ele = self.queue.pop(0)
return ele
def returnQueue(self):
return self.queue
if __name__ == '__main__':
queue = Queue(10)
for i in xrange(5):
queue.push(i)
print queue.pop(), queue.queue
然后，就是计算器的整个主程序：
#python
#coding=utf-8
from stack import Stack
from queue import Queue
class RailExpress():
def __init__(self, express):
self.fontExpress = express
self.railExpress = []
self.size = len(express)
self.stack = Stack(self.size)
self.queue = Queue(self.size)
self.level = {'+': 1, '-': 1, '*': 2, '/': 2, '(': 3, ')': 3}
self.operators = ['+', '-', '*', '/', '(', ')']
self.makeRailExpress()
def makeRailExpress(self):
for i in self.fontExpress:
if i in self.operators:
if i is self.operators[-1]:
ele = self.stack.pop()
while ele is not self.operators[-2]:
self.queue.push(ele)
ele = self.stack.pop()
if self.stack.isEmpty():
break
elif i is self.operators[-2]:
self.stack.push(i)
else:
if not self.stack.isEmpty():
while self.stack.returnFristEle() is not self.operators[-2] and self.level[self.stack.returnFristEle()] >= self.level[i]:
ele = self.stack.pop()
self.queue.push(ele)
if self.stack.isEmpty():
break
self.stack.push(i)
else:
self.queue.push(i)
if not self.stack.isEmpty():
stack = self.stack.returnStack()
stack.reverse()
self.queue.returnQueue().extend(stack)
class CheckExpress():
def __init__(self, express):
if len(express) > 10000:
sys.exit(0)
self.express = express
def checkExpress(self):
express = []
count = -1
for each in self.express:
if (each >= '0') and (each <= '9') or (each == '.'):
length = len(express)
if length == 0:
express.append(each)
count += 1
elif (express[count] >= '0') and (express[count] <= '999999') or (each == '.'):
length = len(express)
express[length - 1] = express[length - 1] + each
else:
express.append(each)
count += 1
else:
if each == '+' or each == '-' or each == '*' or each == '/' or each == '(' or each == ')':
express.append(each)
count += 1
return express
class Calculator():
def __init__(self, express):
self.express = express
size = len(express)
self.stack = Stack(size)
self.result = None
self.operatorRailExpress()
def operatorRailExpress(self):
for each in self.express:
if (each >= '0') and (each <= '999999'):
self.stack.push(each)
else:
twoOperator = self.stack.pop()
oneOperator = self.stack.pop()
temp = self.calculator(oneOperator, twoOperator, each)
self.stack.push(temp)
self.result = self.stack.returnFristEle()
def calculator(self, one, two, operator):
operatorDict = {'+': self.plus, '-': self.reduction, '*': self.multiplicate, '/': self.devision}
temp = operatorDict[operator](one, two)
return temp
def plus(self, one, two):
return float(one)+float(two)
def reduction(self, one, two):
return float(one)-float(two)
def multiplicate(self, one, two):
return float(one)*float(two)
def devision(self, one, two):
return float(one)/float(two)
class ConnectView():
def __init__(self, model):
self._model = model
def calculator(self):
express = CheckExpress(self._model.result).checkExpress()
if len(express) == 1:
sys.exit(0)
rail = RailExpress(express)
queue = rail.queue.returnQueue()
if len(queue) == 1:
sys.exit(0)
calculate = Calculator(queue)
self._model.result = str(calculate.result)
import sys
if __name__ == '__main__':
express = raw_input('输入表达式：')
express = CheckExpress(express).checkExpress()
if len(express) == 1:
sys.exit(0)
rail = RailExpress(express)
queue = rail.queue.returnQueue()
if len(queue) == 1:
print int(queue[0])
sys.exit(0)
calculate = Calculator(queue)
print calculate.result
上面代码分析如下：
1.中缀表达式转后缀表达式的方法：
⑴.遇到操作数：直接输出（添加到后缀表达式中）
⑵.栈为空时，遇到运算符，直接入栈
⑶.遇到左括号：将其入栈
⑷.遇到右括号：执行出栈操作，并将出栈的元素输出，直到弹出栈的是左括号，左括号不输出。
⑸.遇到其他运算符：加减乘除：弹出所有优先级大于或者等于该运算符的栈顶元素，然后将该运算符入栈
⑹.最终将栈中的元素依次出栈，输出。
2.首先解释CheckExpress,这个函数主要是将表达式中的改为标准的表达式，将每个元素加入列表中，这里的每个元素只包括“数字”和“+-*/”，空格或者其它的字符会自动过滤。当只输入一个有效字符时，就会终止程序。
3.RailExpress就是求后缀表达式，程序部分的核心；
4.Calculator就是计算后缀表达式的值。
在此基础上，鄙人用GTK，写了一个简易的计算器界面。算是给这个计算器程序，结了一个尾。界面程序就不贴了~~有意者我们可以私聊~~~嘿嘿·
由于新手一枚，代码质量确实有限。但是，人都是在不断的磨砺中成长，欢迎大家吐槽~~~
