64 lines
1.2 KiB
Ruby
64 lines
1.2 KiB
Ruby
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descr=%{
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The first two consecutive numbers to have two distinct prime factors are:
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14 = 2 × 7
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15 = 3 × 5
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The first three consecutive numbers to have three distinct prime factors are:
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644 = 2² × 7 × 23
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645 = 3 × 5 × 43
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646 = 2 × 17 × 19.
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Find the first four consecutive integers to have four distinct primes factors.
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What is the first of these numbers?
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}
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thoughts=%{
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Loop for each number and find it's prime number decomposition (there is no shortcut doing this)
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}
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puts "Read primes"
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$primes=File.read("firsts_1MM_primes.txt").split().collect! { |p| p.to_i }
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# the uniq is to transform [2,2,3] into [2,3]
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def prime_decomposition(n)
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if n <= 1
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return []
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end
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$primes.each do |p|
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if n % p == 0
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return ( prime_decomposition(n/p) << p ).uniq
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end
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end
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end
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size=4
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buff=[]
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(2..size).each do |n|
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buff <<= prime_decomposition(n).length
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end
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n=size+1
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while true
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buff <<= prime_decomposition(n).length
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found=true
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buff.each do |l|
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if l != size
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found=false
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break
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end
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end
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if n%1000 == 0
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print "** #{n}: "
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p buff
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end
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break if found
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buff.shift
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n+=1
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end
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puts "Solution = #{n+1-size}"
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