Fix multilingual content typos (#1958)

en/codes/ruby/chapter_backtracking/permutations_ii.rb

@@ -4,6 +4,8 @@ Created Time: 2024-05-22
 Author: Xuan Khoa Tu Nguyen (ngxktuzkai2000@gmail.com)
 =end
 
+require 'set'
+
 ### Backtracking: permutations II ###
 def backtrack(state, choices, selected, res)
   # When the state length equals the number of elements, record the solution

en/codes/ruby/chapter_searching/binary_search_insertion.rb

@@ -39,7 +39,7 @@ def binary_search_insertion(nums, target)
     elsif nums[m] > target
       j = m - 1 # target is in the interval [i, m-1]
     else
-      j = m - 1 # The first element less than target is in the interval [i, m-1]
+      j = m - 1 # The rightmost element less than target is in the interval [i, m-1]
     end
   end