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

* [feat] add ruby code - chapter backtracking

* feat: add ruby code block - chapter backtracking

codes/ruby/chapter_backtracking/permutations_i.rb

@@ -0,0 +1,46 @@
+=begin
+File: permutations_i.rb
+Created Time: 2024-05-22
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 回溯算法：全排列 I ###
+def backtrack(state, choices, selected, res)
+  # 当状态长度等于元素数量时，记录解
+  if state.length == choices.length
+    res << state.dup
+    return
+  end
+
+  # 遍历所有选择
+  choices.each_with_index do |choice, i|
+    # 剪枝：不允许重复选择元素
+    unless selected[i]
+      # 尝试：做出选择，更新状态
+      selected[i] = true
+      state << choice
+      # 进行下一轮选择
+      backtrack(state, choices, selected, res)
+      # 回退：撤销选择，恢复到之前的状态
+      selected[i] = false
+      state.pop
+    end
+  end
+end
+
+### 全排列 I ###
+def permutations_i(nums)
+  res = []
+  backtrack([], nums, Array.new(nums.length, false), res)
+  res
+end
+
+### Driver Code ###
+if __FILE__ == $0
+  nums = [1, 2, 3]
+
+  res = permutations_i(nums)
+
+  puts "输入数组 nums = #{nums}"
+  puts "所有排列 res = #{res}"
+end