feat: Add Ruby code - chapter "computational complexity" (#1212)

* feat: add ruby code - chapter computational complexity

* feat: add ruby code blocks

codes/ruby/chapter_computational_complexity/recursion.rb

@@ -0,0 +1,69 @@
+=begin
+File: recursion.rb
+Created Time: 2024-03-30
+Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
+=end
+
+### 递归 ###
+def recur(n)
+  # 终止条件
+  return 1 if n == 1
+  # 递：递归调用
+  res = recur n - 1
+  # 归：返回结果
+  n + res
+end
+
+### 使用迭代模拟递归 ###
+def for_loop_recur(n)
+  # 使用一个显式的栈来模拟系统调用栈
+  stack = []
+  res = 0
+
+  # 递：递归调用
+  for i in n.downto(0)
+    # 通过“入栈操作”模拟“递”
+    stack << i
+  end
+  # 归：返回结果
+  while !stack.empty?
+    res += stack.pop
+  end
+
+  # res = 1+2+3+...+n
+  res
+end
+
+### 尾递归 ###
+def tail_recur(n, res)
+  # 终止条件
+  return res if n == 0
+  # 尾递归调用
+  tail_recur n - 1, res + n
+end
+
+### 斐波那契数列：递归 ###
+def fib(n)
+  # 终止条件 f(1) = 0, f(2) = 1
+  return n - 1 if n == 1 || n == 2
+  # 递归调用 f(n) = f(n-1) + f(n-2)
+  res = fib(n - 1) + fib(n - 2)
+  # 返回结果 f(n)
+  res
+end
+
+### Driver Code ###
+
+n = 5
+
+res = recur n
+puts "\n递归函数的求和结果 res = #{res}"
+
+res = for_loop_recur n
+puts "\n使用迭代模拟递归求和结果 res = #{res}"
+
+res = tail_recur n, 0
+puts "\n尾递归函数的求和结果 res = #{res}"
+
+res = fib n
+puts "\n斐波那契数列的第 #{n} 项为 #{res}"