Python中的Kattis波兰语符号挑战

Question

我正试着做这个polish notation challenge on kattis.com。问题是，我觉得我已经完成了他们要求的一切，并且我已经试着修复我能想到的一切。我甚至查阅了一些其他人的解决方案，虽然他们的解决方案更干净，但我想在学习的过程中继续我的解决方案

为什么例如this person's code可以工作，而不是我的

这是我目前的代码：

import sys
case = 1
valid_ints = set([str(i) for i in range(-10,11)])


def simplify(index, myLine, processed):
  while index+1 > 0:
      if (myLine[index] == "+" or myLine[index] == "-" or myLine[index] == "*") and index < len(myLine)-2:
        if myLine[index+1] in valid_ints and myLine[index+2] in valid_ints:
          try:
            processed = myLine[index+3:] + processed
            a = str(myLine[index+1] + myLine[index] + myLine[index+2])
            processed.insert(0, str(eval(a)))
            del myLine[index:]
          except:
            processed = [myLine[index], myLine[index+1], myLine[index+2]] + processed
            del myLine[index:]
      elif len(myLine) < 3:
        processed = myLine + processed
        del myLine[index]
      index -= 1
  processed = myLine + processed
  return processed

for line in sys.stdin:
    myLine = line.split()
    processed = []
    index = len(myLine)-1
    savedprocessed = []
    processed = simplify(index, myLine, processed)
    while True:
      if savedprocessed == processed:
        break
      else:
        savedprocessed = []
        savedprocessed += processed
        processed = simplify(len(processed)-1, processed, [])
        
    result = " ".join(savedprocessed)
    print("Case " + str(case) + ": " + result)
    case += 1
    if case > 5:
      break

Answer 1

您正在为Python带来一些其他的语言风格，这是不必要的，因为Python更灵活

我已经尽可能地简化了

在空白处拆分输入字符串，并迭代标记

对于表达式中的每个运算符，将list推送到堆栈上，并将运算符及其操作数附加到list

现在将每个list从堆栈中弹出并处理list

def simplify(exp):                                                                                                                                                        
    stack1 = []                                                                                                                                                           
    ops = set('+*-')                                                                                                                                                      
    for token in exp.split():                                                                                                                                             
        if token in ops:                                                                                                                                                  
            stack1.append([])                                                                                                                                             
        stack1[-1].append(token)                                                                                                                                          
                                                                                                                                                                          
    stack2 = []                                                                                                                                                           
    while stack1:                                                                                                                                                         
        top = stack1.pop()                                                                                                                                                
        while len(top) < 3 and stack2:                                                                                                                                    
            top.append(stack2.pop())                                                                                                                                      
        if any(x.isalpha() for x in top):                                                                                                                                 
            simplified = ' '.join(top)                                                                                                                                    
        else:                                                                                                                                                             
            top[0], top[1] = top[1], top[0]                                                                                                                               
            simplified = str(eval(''.join(top)))                                                                                                                          
        stack2.append(simplified)                                                                                                                                         
    return simplified                                                                                                                                                     

exp = '* - 6 + x -6 - - 9 6 * 0 c'                                                                                                                                        
print(exp)
simplify(exp)                        

产出

* - 6 + x -6 - - 9 6 * 0 c
* - 6 + x -6 - - 3 * 0 c