20 lines
465 B
Ruby
20 lines
465 B
Ruby
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require 'set' # Set: Fast array lookup / Simple existence hash
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@seen_numbers = Set.new
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@happy_numbers = Set.new
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def happy?(n)
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return true if n == 1 # Base case
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return @happy_numbers.include?(n) if @seen_numbers.include?(n) # Use performance cache, and stop unhappy cycles
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@seen_numbers << n
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digit_squared_sum = n.digits.sum{|n| n*n}
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if happy?(digit_squared_sum)
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@happy_numbers << n
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true # Return true
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else
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false # Return false
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end
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end
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