前序算数表达式

最新推荐文章于 2025-06-10 08:29:53 发布

aircoder

最新推荐文章于 2025-06-10 08:29:53 发布

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分类专栏： python算法文章标签： python

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本文介绍了一个简单的算数表达式解析和计算程序。该程序能够处理包含括号、加减乘除运算的表达式，并通过栈来实现操作符和操作数的管理。通过逐字符扫描输入的表达式，程序能正确地执行运算并返回最终结果。

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#!/usr/bin/python
#coding=utf-8

import sys
sys.path.append('/home/administrator/python_dir/tools')
from Stack import Stack

num_stack = Stack()
operator_stack = Stack()
brackets_stack = Stack()

import char_tools
def execute_express(press):
i=0;
while i < len(press):
char = press[i]
if char_tools.str_is_number(press[i]):
j=exe_num(press,i)
if j > i and j != -1:
num_stack.push(press[i:j])
i=j
else:
num_stack.push(press[i])
i = i+1

elif char_tools.str_is_operator(press[i]):
operator_stack.push(press[i])
i = i+1
elif press[i] == '(':
brackets_stack.push(press[i])
i = i+1
elif press[i] == ')':
if brackets_stack.isEmpty() or operator_stack.isEmpty():
print '有错误'
raise RuntimeError('有错误')
else:
value = exe_num_value(num_stack.pop(),num_stack.pop(),operator_stack.pop())
num_stack.push(value)
i = i+1
else:
i = i+1

def exe_num_value(num0,num1,operator):
value = None
if operator == '+':
value = int(num0)+int(num1)
elif operator == '-':
value = int(num1)-int(num0)
elif operator == '*':
value = int(num1)*int(num0)
elif operator == '/':
value = int(num1)/int(num0)
else :
print '出现错误!\t\n'
raise RuntimeError('有错误')
return value

def exe_num(press,i):

while i <len(press):
if char_tools.str_is_number(press[i]):
i = i+1
continue
else:
return i

return -1

if __name__ == '__main__':

print '算数表达式计算'
execute_express('((*2 2)+(+ 1 2 ))')
print num_stack.pop()