Odd Occurrences In Array

Odd Occurrences In Array

Now that I found this...  Lets do the next one.

https://codility.com/programmers/lessons/2-arrays/odd_occurrences_in_array/

a = [9,3,9,3,9,7,9]
a.group_by(&:itself).inject(0){|hash, (k,v)| v.first if v.size.odd?} 
# Could also use transform_values instead of inject on Ruby 2.4

Turns out this one is easy with XOR exlusive or operator ^.

a.inject(:^)

Which does:

9.to_s(2)      #1001 #9
(9^0).to_s(2)  #1001 #9
3.to_s(2)      # 111 #3
(9^3).to_s(2)  #1010 #10
9.to_s(2)      #1001 #9
(10^9).to_s(2) #  11 #3
3.to_s(2)      # 111 #3
(10^3).to_s(2) #1001 #9
9.to_s(2)      #1001 #9
(9^9).to_s(2)  #   0 #0
7.to_s(2)      # 111 #7
(9^7).to_s(2)  #1110 #14
9.to_s(2)      #1001 #9
(14^9).to_s(2) # 111 #7