a = ["A", "B", "C", "B", "A"]
a.detect{ |e| a.count(e) > 1 } # => ['A', 'B']Ruby: How to find and return a duplicate value in array? - stackoverflow
a = ["A", "B", "C", "B", "A"]
a.detect{ |e| a.count(e) > 1 } # => ['A', 'B']Ruby: How to find and return a duplicate value in array? - stackoverflow