Add the chapter of backtracking. (#459)

codes/python/chapter_backtracking/preorder_find_paths.py

@@ -0,0 +1,42 @@
+"""
+File: preorder_find_paths.py
+Created Time: 2023-04-15
+Author: Krahets (krahets@163.com)
+"""
+
+import sys, os.path as osp
+
+sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
+from modules import *
+
+
+def pre_order(root: TreeNode) -> None:
+    """前序遍历"""
+    if root is None:
+        return
+    # 尝试
+    path.append(root)
+    if root.val == 7:
+        # 记录解
+        res.append(list(path))
+    pre_order(root.left)
+    pre_order(root.right)
+    # 回退
+    path.pop()
+    return
+
+
+"""Driver Code"""
+if __name__ == "__main__":
+    root = list_to_tree([1, 7, 3, 4, 5, 6, 7])
+    print("\n初始化二叉树")
+    print_tree(root)
+
+    # 前序遍历
+    path = list[TreeNode]()
+    res = list[list[TreeNode]]()
+    pre_order(root)
+
+    print("\n输出所有根节点到节点 7 的路径")
+    for path in res:
+        print([node.val for node in path])