Add implementation of array binary tree.

Rewrite the tree serialization and deserialization methods.
Add applications of array and linked list.

codes/python/modules/tree_node.py

@@ -0,0 +1,80 @@
+"""
+File: tree_node.py
+Created Time: 2021-12-11
+Author: Krahets (krahets@163.com)
+"""
+
+from collections import deque
+
+
+class TreeNode:
+    """二叉树节点类"""
+
+    def __init__(self, val: int = 0):
+        self.val: int = val  # 节点值
+        self.height: int = 0  # 节点高度
+        self.left: TreeNode | None = None  # 左子节点引用
+        self.right: TreeNode | None = None  # 右子节点引用
+
+    # 序列化编码规则请参考：
+    # https://www.hello-algo.com/chapter_tree/array_representation_of_tree/
+    # 二叉树的数组表示：
+    # [1, 2, 3, 4, None, 6, 7, 8, 9, None, None, 12, None, None, 15]
+    # 二叉树的链表表示：
+    #             /——— 15
+    #         /——— 7
+    #     /——— 3
+    #    |    \——— 6
+    #    |        \——— 12
+    # ——— 1
+    #     \——— 2
+    #        |    /——— 9
+    #         \——— 4
+    #             \——— 8
+
+
+def list_to_tree_dfs(arr: list[int], i: int) -> TreeNode | None:
+    """将列表反序列化为二叉树：递归"""
+    # 如果索引超出数组长度，或者对应的元素为 None，返回 None
+    if i < 0 or i >= len(arr) or arr[i] is None:
+        return None
+    # 构建当前节点
+    root = TreeNode(arr[i])
+    # 递归构建左右子树
+    root.left = list_to_tree_dfs(arr, 2 * i + 1)
+    root.right = list_to_tree_dfs(arr, 2 * i + 2)
+    return root
+
+
+def list_to_tree(arr: list[int]) -> TreeNode | None:
+    """将列表反序列化为二叉树"""
+    return list_to_tree_dfs(arr, 0)
+
+
+def tree_to_list_dfs(root: TreeNode, i: int, res: list[int]) -> list[int]:
+    """将二叉树序列化为列表：递归"""
+    if root is None:
+        return
+    if i >= len(res):
+        res += [None] * (i - len(res) + 1)
+    res[i] = root.val
+    tree_to_list_dfs(root.left, 2 * i + 1, res)
+    tree_to_list_dfs(root.right, 2 * i + 2, res)
+
+
+def tree_to_list(root: TreeNode | None) -> list[int]:
+    """将二叉树序列化为列表"""
+    res = []
+    tree_to_list_dfs(root, 0, res)
+    return res
+
+
+def get_tree_node(root: TreeNode | None, val: int) -> TreeNode | None:
+    """Get a tree node with specific value in a binary tree"""
+    if not root:
+        return
+    if root.val == val:
+        return root
+    left: TreeNode | None = get_tree_node(root.left, val)
+    right: TreeNode | None = get_tree_node(root.right, val)
+    return left if left else right