297. 二叉树的序列化与反序列化
letcode 297题思路
- 二叉树的序列化与反序列化
序列化是将一个数据结构或者对象转换为连续的比特位的操作,进而可以将转换后的数据存储在一个文件或者内存中,同时也可以通过网络传输到另一个计算机环境,采取相反方式重构得到原数据。
请设计一个算法来实现二叉树的序列化与反序列化。这里不限定你的序列 / 反序列化算法执行逻辑,你只需要保证一个二叉树可以被序列化为一个字符串并且将这个字符串反序列化为原始的树结构雅思分数。
示例:
你可以将以下二叉树:
1 / \ 2 3 / \ 4 5
序列化为 “[1,2,3,null,null,4,5]”
题解思路:
- BFS
class Codec : def serialize ( self , root ) : """Encodes a tree to a single string.
:type root: TreeNode
:rtype: str
""" if ( root is None ) : return [ ] res = [ ] from collections import deque
queue = deque ( [ root ] ) while ( queue ) : tmp = queue . popleft ( ) if ( tmp is None ) : res . append ( '#' ) else : res . append ( str ( tmp . val ) ) queue . append ( tmp . left ) queue . append ( tmp . right ) return ',' . join ( res ) def deserialize ( self , data ) : """Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
""" from collections import deque if ( data == '' or data == [ ] ) : return None queue = deque ( [ ] ) data = data . split ( ',' ) root = TreeNode ( data [ 0 ] ) queue . append ( root ) i = 1 while ( queue ) : tmp = queue . popleft ( ) if ( data [ i ] != '#' ) : tmp . left = TreeNode ( data [ i ] ) queue . append ( tmp . left ) i += 1 if ( data [ i ] != '#' ) : tmp . right = TreeNode ( data [ i ] ) queue . append ( tmp . right ) i += 1 return root
- 递归思路
class Codec : def serialize ( self , root ) : """Encodes a tree to a single string.
:type root: TreeNode
:rtype: str
""" res = [ ] def helper ( root ) : if ( not root ) : res . append ( '#' ) return res . append ( str ( root . val ) ) helper ( root . left ) helper ( root . right ) helper ( root ) return ',' . join ( res ) def deserialize ( self , data ) : """Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
""" data = data . split ( ',' ) def helper ( index ) : if ( data [ index ] == '#' ) : return ( index , None ) else : root = TreeNode ( data [ index ] ) l , root . left = helper ( 1 + index ) r , root . right = helper ( l + 1 ) return ( r , root ) l , root = helper ( 0 ) return root
- 巧用next方法
class Codec : def serialize ( self , root ) : """Encodes a tree to a single string.
:type root: TreeNode
:rtype: str
""" res = [ ] def helper ( root ) : if ( not root ) : res . append ( '#' ) return res . append ( str ( root . val ) ) helper ( root . left ) helper ( root . right ) helper ( root ) return ',' . join ( res ) def deserialize ( self , data ) : """Decodes your encoded data to tree.
:type data: str
:rtype: TreeNode
""" vals = iter ( data . split ( ',' ) ) def helper ( ) : a = next ( vals ) if ( a == '#' ) : return None else : root = TreeNode ( a ) print ( root . val ) root . left = helper ( ) root . right = helper ( ) return root
root = helper ( ) return root