The sieve of Sundaram: Difference between revisions
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=={{header|Ruby}}== |
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Based on the Python code from the Wikipedia lemma. |
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<lang ruby>def sieve_of_sundaram(upto) |
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n = (2.4 * upto * Math.log(upto)) / 2 |
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k = (n - 3) / 2 + 1 |
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bools = [true] * k |
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(0..(Integer.sqrt(n) - 3) / 2 + 1).each do |i| |
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p = 2*i + 3 |
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s = (p*p - 3) / 2 |
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(s..k).step(p){|j| bools[j] = false} |
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end |
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bools.filter_map.each_with_index {|b, i| (i + 1) * 2 + 1 if b } |
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end |
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p sieve_of_sundaram(100) |
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n = 1_000_000 |
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puts "\nThe #{n}th sundaram prime is #{sieve_of_sundaram(n)[n-1]}" |
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</lang> |
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{{out}} |
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<pre>[3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541, 547] |
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The 1000000th sundaram prime is 15485867 |
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</pre> |
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=={{header|Wren}}== |
=={{header|Wren}}== |
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