Add multilingual exercise code (#1959)

Replace the exercise pages' Python-only snippets with source-backed implementations for the 13 visible programming languages, and localize reader-facing comments by site language. Zig remains out of scope.

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ja/codes/ruby/chapter_computational_complexity/complexity_exercises.rb

@@ -0,0 +1,55 @@
+=begin
+File: complexity_exercises.rb
+Created Time: 2026-08-18
+Author: Hello Algo Team
+=end
+
+### 反復による総和 ###
+def sum_iter(n)
+  res = 0
+  for i in 1..n
+    res += i
+  end
+  res
+end
+
+### 再帰による総和 ###
+def sum_recur(n)
+  return 1 if n == 1
+
+  n + sum_recur(n - 1)
+end
+
+### 線形時間のループ ###
+def linear_loop(n)
+  res = 0
+  for i in 0...n
+    res += i
+  end
+  res
+end
+
+### 二次時間のループ ###
+def quadratic_loop(n)
+  res = 0
+  for i in 0...n
+    for j in i...n
+      res += j
+    end
+  end
+  res
+end
+
+### 対数時間のループ ###
+def logarithmic_loop(n)
+  n /= 2 while n > 1
+  n
+end
+
+if __FILE__ == $0
+  raise 'sum check failed' unless sum_iter(1) == 1 && sum_recur(1) == 1
+  raise 'sum check failed' unless sum_iter(4) == 10 && sum_recur(4) == 10
+  raise 'linear check failed' unless linear_loop(4) == 6
+  raise 'quadratic check failed' unless quadratic_loop(4) == 20
+  raise 'logarithmic check failed' unless logarithmic_loop(4) == 1 && logarithmic_loop(5) == 1
+end