python代数式括号有效性检验示例代码

思路：

利用栈实现代数式中括号有效行的的检验：

代码：

class mychain(object): #利用链表建立栈，链表为父类
 length=0
 def __init__(self,value=None,next=None):#创建链表，长度并不包含头部
  self.value=value
  self.next=next
  #mychain.length=mychain.length+1
 def append(self,value=None):
  while self.next!=None:
   self=self.next
  self.next=mychain(value)
  mychain.length=mychain.length+1 #追加时，链表长度增加
 def travle(self):#遍历链表
  print(self.value)
  if self.next!=None:
   self.next.travle()
 def drop (self,value):#删除特定值的第一个匹配节点
  while self.next!=None:
   if self.next.value!=value:
    self=self.next
   else:
    self.next=self.next.next
    mychain.length=mychain.length-1 #删除时，链表长度减小
    break
 def pop(self):#删除未节点
  if self.next!=None:#并不删除头结点
   while self.next.next!=None:
    self=self.next
   self.next=None
   mychain.length=mychain.length-1#弹出为节点，并减小长度，头结点不弹出



class stock(mychain):#栈类
 bottom=None 　　#栈底
 top=None　　　　　#栈顶
 n_count=0　　　　#计数
 def Max(self):　　#占中最大值
  if self.next!=None:
   tmp = self.next.value
   while self.next.next!=None:
    self=self.next
    if self.next.value>tmp:
     tmp=self.next.value
   return tmp
  else:
   print('栈为空！')
 def Min(self):#栈中的最小值
  if self.next!=None:
   tmp = self.next.value
   while self.next.next!=None:
    self=self.next
    if self.next.value<tmp:
     tmp=self.next.value
   return tmp
  else:
   print('栈为空！')

 def push(self,value): #压栈
  while self.next != None:
   self = self.next
  self.next = mychain(value)
  stock.top=self.next
  stock.length=stock.length+1
  stock.n_count=stock.n_count+1
 def __init__(self,value='',next=None):
  self.value=value
  self.next=next
  stock.bottom=self
  stock.top=self
  #stock.n_count=stock.n_count+1
  #stock.length=stock.length+1
 def append(self,value=''):#取消追加函数
  print('请使用Push()!')
 def pop(self):
  if self.next!=None:#并不删除头结点
   while self.next.next!=None:
    self=self.next
   self.next=None
   stock.top=self
   stock.length=stock.length-1#弹出为节点，并减小长度，头结点不弹出
class solution(object):
 def validationofbrackets(self,astr=''):#检验串中的括号合法性
  braketsstock=stock()
  for i in astr:
   if i in ['{','(','[']:
    braketsstock.push(i)
   else:
    if i==')':
     if braketsstock.top.value=='(':
      braketsstock.pop()
     else:
      return False
    elif i==']':
     if braketsstock.top.value=='[':
      braketsstock.pop()
     else:
      return False
    elif i=='}':
     if braketsstock.top.value=='{':
      braketsstock.pop()
     else:
      return False
    else:
     pass
  print(astr)
  print(braketsstock.length)
  if braketsstock.length==0:
   return True
  else:
   return False

运行：

bstr='([{((({{}})))}]){{}}{{}{}{}[][]()(123)(((sin5)))}'
f=solution()
print(f.validationofbrackets(bstr))

总结