Tuesday, May 05, 2009

JavaOne Talk: Ruby Prime Sieve

See this post for an explanation on why this code is being shown and what kind of responses would be useful. See this post for the Java algorithm to compare against.

class RubyPrimes
attr_accessor :cnt, :primes
def initialize(n)
@primes = Array.new(n,0)
@cnt = 0
i = 2
max = calcSize
nums = Array.new(max,true)
while (i < max && @cnt < @primes.length)
p = i
if (nums[i])
@primes[@cnt] = p
@cnt += 1
(p .. (max/p)).each{ |j| nums[p*j] = false }
end
i += 1
end
end
def calcSize
max = 2
max = max * 2 while ( max/Math.log(max) < @primes.length)
max
end
def last
@primes[@cnt -1]
end
end

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