feat: Add Ruby code - chapter "Backtracking" (#1373)

* [feat] add ruby code - chapter backtracking

* feat: add ruby code block - chapter backtracking

codes/ruby/chapter_backtracking/preorder_traversal_iii_compact.rb

@@ -0,0 +1,42 @@
+=begin
+File: preorder_traversal_iii_compact.rb
+Created Time: 2024-05-22
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+require_relative '../utils/tree_node'
+require_relative '../utils/print_util'
+
+### 前序遍历：例题三 ###
+def pre_order(root)
+  # 剪枝
+  return if !root || root.val == 3
+
+  # 尝试
+  $path.append(root)
+
+  # 记录解
+  $res << $path.dup if root.val == 7
+
+  pre_order(root.left)
+  pre_order(root.right)
+
+  # 回退
+  $path.pop
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  root = arr_to_tree([1, 7, 3, 4, 5, 6, 7])
+  puts "\n初始化二叉树"
+  print_tree(root)
+
+  # 前序遍历
+  $path, $res = [], []
+  pre_order(root)
+
+  puts "\n输出所有根节点到节点 7 的路径，路径中不包含值为 3 的节点"
+  for path in $res
+    p path.map { |node| node.val }
+  end
+end