Rearrange the chapters.

Start to translate codes from Java to Python.

codes/python/include/binary_tree.py

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+'''
+File: binary_tree.py
+Created Time: 2021-12-11
+Author: Krahets (krahets@163.com)
+'''
+
+import collections
+
+class TreeNode:
+    """Definition for a binary tree node
+    """    
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+def list_to_tree(arr):
+    """Generate a binary tree with a list
+
+    Args:
+        arr ([type]): [description]
+
+    Returns:
+        [type]: [description]
+    """
+    if not arr:
+        return
+    i = 1
+    root = TreeNode(int(arr[0]))
+    queue = collections.deque()
+    queue.append(root)
+    while queue:
+        node = queue.popleft()
+        if arr[i] != None:
+            node.left = TreeNode(int(arr[i]))
+            queue.append(node.left)
+        i += 1
+        if arr[i] != None:
+            node.right = TreeNode(int(arr[i]))
+            queue.append(node.right)
+        i += 1
+    return root
+
+def tree_to_list(root):
+    """Serialize a tree into an array
+
+    Args:
+        root ([type]): [description]
+
+    Returns:
+        [type]: [description]
+    """    
+    if not root: return []
+    queue = collections.deque()
+    queue.append(root)
+    res = []
+    while queue:
+        node = queue.popleft()
+        if node:
+            res.append(node.val)
+            queue.append(node.left)
+            queue.append(node.right)
+        else: res.append(None)
+    return res
+
+def get_tree_node(root, val):
+    """Get a tree node with specific value in a binary tree
+
+    Args:
+        root ([type]): [description]
+        val ([type]): [description]
+
+    Returns:
+        [type]: [description]
+    """    
+    if not root:
+        return
+    if root.val == val:
+        return root
+    left = get_tree_node(root.left, val)
+    right = get_tree_node(root.right, val)
+    return left if left else right