add tree_DFS python code

codes/python/chapter_tree/binary_tree_dfs.py

@@ -8,3 +8,39 @@ import sys, os.path as osp
 sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
 from include import *
 
+# 定义一个result数组用来存储遍历的结果
+result = []
+
+# 前序遍历
+def preorder(root):
+    if root == None:
+        return []
+    ·
+    # 访问顺序：根结点 -> 左子树 -> 右子树
+
+    result.append(root.val)
+    preorder(root.left)
+    preorder(root.right)
+
+
+# 中序遍历
+def inorder(root):
+    if root == None:
+        return []
+
+    # 访问顺序：左子树 -> 根结点 -> 右子树
+    
+    inorder(root.left)
+    result.append(root.val)
+    inorder(root.right)
+
+# 后序遍历
+def postorder(root):
+    if root == None:
+        return []
+
+    # 访问顺序：左子树 -> 右子树 -> 根结点
+
+    postorder(root.left)
+    postorder(root.right)
+    result.append(root.val)