new tasks

Task/Balanced_brackets/Ruby/balanced_brackets.rb

@@ -0,0 +1,24 @@
+re = /\A     # beginning of string
+  (?<bb>     # begin capture group <bb>
+    \[       #   literal [
+    \g<bb>*  #   zero or more <bb>
+    \]       #   literal ]
+  )*         # end group, zero or more such groups
+\z/x         # end of string
+
+(0..9).each do |i|
+  s = "[]" * i
+
+  # There is no String#shuffle! method.
+  # This is a Knuth shuffle.
+  (s.length - 1).downto(1) do |a; b|
+    b = rand(a + 1)
+    s[a], s[b] = s[b], s[a]
+  end
+
+  puts((s =~ re ? " OK: " : "bad: ") + s)
+end
+
+["[[]", "[]]", "[letters]"].each do |s|
+  puts((s =~ re ? " OK: " : "bad: ") + s)
+end