Subtract values as many times as they appear in the other array, or any Enumerable:
class Array
# Subtract each passed value once:
# %w(1 2 3 1).subtract_once %w(1 1 2) # => ["3"]
# [ 1, 1, 2, 2, 3, 3, 4, 5 ].subtract_once([ 1, 2, 4 ]) => [1, 2, 3, 3, 5]
# Time complexity of O(n + m)
def subtract_once(values)
counts = values.inject(Hash.new(0)) { |h, v| h[v] += 1; h }
reject { |e| counts[e] -= 1 unless counts[e].zero? }
end
Subtract each unique value once:
require 'set'
class Array
# Subtract each unique value once:
# %w(1 2 2).subtract_once_uniq %w(1 2 2) # => [2]
# Time complexity of O((n + m) * log m)
def subtract_once_uniq(values)
# note that set is implemented
values_set = Set.new values.to_a
reject { |e| values_set.delete(e) if values_set.include?(e) }
end
end