39 lines
914 B
Ruby
39 lines
914 B
Ruby
descr=%{
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The number, 197, is called a circular prime because all rotations of the digits: 197, 971, and 719, are themselves prime.
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There are thirteen such primes below 100: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, 79, and 97.
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How many circular primes are there below one million?
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}
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puts "Read primes"
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primes=File.read("firsts_1MM_primes.txt").split().collect! { |p| p.to_i }
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is_prime={}
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puts "Init datastructure"
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primes.each do |p|
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is_prime[p]=true
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end
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puts "search circulars"
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circular=[]
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primes.each do |p|
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arr=p.to_s.split('')
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len=arr.length
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number=arr.join('').to_i
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i=0
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# puts "#{len} #{number} #{i}"
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while i<len && is_prime[number]
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x=arr.shift()
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arr.push(x)
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number=arr.join('').to_i
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# puts "> #{number}"
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i+=1
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end
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if i==len
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puts "circular #{p}"
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circular <<= p
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end
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end
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puts "NB: #{circular.length}"
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