49 lines
1.1 KiB
Ruby
49 lines
1.1 KiB
Ruby
descr=%{
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The prime 41, can be written as the sum of six consecutive primes:
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41 = 2 + 3 + 5 + 7 + 11 + 13
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This is the longest sum of consecutive primes that adds to a prime below one-hundred.
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The longest sum of consecutive primes below one-thousand that adds to a prime, contains 21 terms, and is equal to 953.
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Which prime, below one-million, can be written as the sum of the most consecutive primes?
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}
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require "primes"
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po = Primes.new(1)
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primes = po.primes
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maxnb=0
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best=0
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min=0
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max=0
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limit=1000000
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initsum=primes.inject(0) {|sum,p| sum+p}
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initnb=primes.length
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primes.reverse.each do |maxp|
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initsum -= maxp
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sum=initsum
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initnb -= 1
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nb = initnb
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next if maxp>limit/21
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primes.each do |minp|
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sum -= minp
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nb -= 1
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next if minp>limit/21
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break if maxp <= minp
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next if sum>limit
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if po.is_prime(sum)
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if nb>maxnb
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best=sum
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maxnb=nb
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min=minp
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max=maxp
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puts %{#{best} #{min}->#{max} (#{maxnb})}
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end
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end
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end
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end
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puts %{BEST: #{best} #{min}->#{max} (#{maxnb})}
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