leetcode1028

 class Solution(object):
     def __init__(self):
         self.List = list()

     def rdfs(self,S):
         if S != '':
             length = len(S)
             depth = len(self.List)
             tempval = ''
             tempdepth = 0
             for i in range(length):
                 s = S[i]
                 if s != '-':
                     tempval += s
                     if i == length - 1:
                         while depth != tempdepth:
                             self.List.pop(-1)
                             depth = len(self.List)
                         parent = self.List[-1]

                         val = int(tempval)
                         t = TreeNode(val)
                         if parent.left == None:
                             parent.left = t
                         elif parent.right == None:
                             parent.right = t

                 else:
                     if tempval != '':
                         while depth != tempdepth:
                             self.List.pop(-1)
                             depth = len(self.List)
                         parent = self.List[-1]

                         val = int(tempval)
                         t = TreeNode(val)
                         if parent.left == None:
                             parent.left = t
                             self.List.append(t)
                             self.rdfs(S[i:])
                         elif parent.right == None:
                             parent.right = t
                             self.List.append(t)
                             self.rdfs(S[i:])
                         break
                     else:
                         tempdepth += 1
         else:
             return None

     def recoverFromPreorder(self, S: str) -> 'TreeNode':
         tempval = ''
         length = len(S)
         for i in range(length):
             s = S[i]
             if s != '-':#数字
                 tempval += s
                 if i == length - 1:
                     val = int(tempval)
                     root = TreeNode(val)

             else:#遇到横线，数字结束
                 val = int(tempval)
                 root = TreeNode(val)
                 self.List.append(root)
                 self.rdfs(S[i:])
                 self.List.pop(-1)
                 return root
         return root