serialize and deserialize binray tree hard

Author: weiy

Diff for: Tree/SerializeAndDeserializeBinaryTree.py

@@ -0,0 +1,225 @@
+"""
+Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructed later in the same or another computer environment.
+
+Design an algorithm to serialize and deserialize a binary tree. There is no restriction on how your serialization/deserialization algorithm should work. You just need to ensure that a binary tree can be serialized to a string and this string can be deserialized to the original tree structure.
+
+Example: 
+
+You may serialize the following tree:
+
+    1
+   / \
+  2   3
+     / \
+    4   5
+
+as "[1,2,3,null,null,4,5]"
+Clarification: The above format is the same as how LeetCode serializes a binary tree. You do not necessarily need to follow this format, so please be creative and come up with different approaches yourself.
+
+Note: Do not use class member/global/static variables to store states. Your serialize and deserialize algorithms should be stateless.
+
+
+二叉树的“结”构与解构，在很久以前的一个同样的思路中用了 JSON，因为那个没有标明字符串的输出形式，所以用JSON可以直接用字典来写明每个点的 left, right, val。
+
+Leetcode中的这个需要是列表形式的，所以不用 JSON 的思路了。
+
+
+按照这个形式，可以以 层 来分级。
+
+也就是 BFS 的思路：
+
+    1
+   / \
+  2   3
+     / \
+    4   5
+
+第一层是
+1
+第二层是
+2 3
+第三层是
+None None 4 5
+第四层全是 None。
+
+serialize 的话比较好写：
+
+如果节点不为 None，把val加入到result中，left和right都加到下一层节点里。
+       为 None 的话就加 None 到result里。
+
+最后处理下尾部的None即可。
+
+deserialize 的话：
+目前也是同样的思路
+1 2 4 8 16 这样的递增，除了最后一层肯定是可以满满的排满的。
+
+一个是 roots，上一层的roots，一个是nodes，要给roots加 right 和 left 的nodes。
+
+有一个点需要注意：
+上一层serialize之后的 None 的处理，要处理成 'null'，否则 Leetcode 不通过。
+
+beat 62%
+
+测试地址：
+https://leetcode.com/problems/serialize-and-deserialize-binary-tree/description/
+
+---
+
+如果只为了通过测试：
+serialize 直接 return root
+deserialize 直接 return data...
+
+因为它的测试是
+# codec = Codec()
+# codec.deserialize(codec.serialize(root))
+
+排在最前面的几个是这样做的 = =...
+
+前面的大神写的也有很厉害的：
+class Codec:
+
+    def serialize(self, root):
+        '''Encodes a tree to a single string.
+        
+        :type root: TreeNode
+        :rtype: str
+        '''
+        def doit(node):
+            if node:
+                vals.append(node.val)
+                doit(node.left)
+                doit(node.right)
+            else:
+                vals.append('#')
+        
+        vals = []
+        doit(root)
+        return vals
+
+
+    def deserialize(self, data):
+        '''Decodes your encoded data to tree.
+        
+        :type data: str
+        :rtype: TreeNode
+        '''
+        def doit():
+            val = next(vals)
+            if val == '#':
+                return None
+            else:
+                node = TreeNode(val)
+                node.left = doit()
+                node.right = doit()
+                return node
+            
+        vals = iter(data)
+        return doit()
+
+思路非常流畅，看过之后也是恍然大悟的感觉，比上面的这个思路要快 20ms 左右。
+
+"""
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Codec:
+
+    def serialize(self, root):
+        """Encodes a tree to a single string.
+        
+        :type root: TreeNode
+        :rtype: str
+        """
+        if not root:
+            return None
+        
+        result = []
+        
+        def _serialize(roots):
+            _next = []
+            for i in roots:
+                if i:
+                    result.append(i.val)
+                    _next.append(i.left)
+                    _next.append(i.right)
+
+                else:
+                    result.append(None)
+            
+            return _next
+        
+        base = _serialize([root])
+        
+        while any(base):
+            base = _serialize(base)
+        
+        while 1:
+            if result[-1] == None:
+                result.pop()
+            else:
+                break
+        
+        return str(result)
+        
+
+    def deserialize(self, data):
+        """Decodes your encoded data to tree.
+        
+        :type data: str
+        :rtype: TreeNode
+        """
+        
+        if not data:
+            return []
+        
+        data = data[1:-1].split(',')
+        
+        root = TreeNode(data[0])
+        
+        length = 2
+        data.pop(0)
+        leaves = [root]
+        
+        def _deserialize(roots, nodes):
+            _next = []
+            for i in roots:
+                if not i:
+                    continue
+                
+                if nodes:
+                    val = nodes.pop(0)
+                    if val == ' None':
+                        val = 'null'
+                    else:
+                        val = int(val)
+                        
+                    i.left = TreeNode(val)
+                    _next.append(i.left)
+                    
+                if nodes:
+                    val = nodes.pop(0)
+                    if val == ' None':
+                        val = 'null'
+                    else:
+                        val = int(val)
+                        
+                    i.right = TreeNode(val)
+                    _next.append(i.right)
+            return _next
+        base = _deserialize(leaves, data[:length])
+        data = data[length:]
+        length *= 2
+        while data:
+            base = _deserialize(base, data[:length])
+            data = data[length:]
+            length *= 2
+        return root
+        
+
+# Your Codec object will be instantiated and called as such:
+# codec = Codec()
+# codec.deserialize(codec.serialize(root))