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- #!/usr/bin/ruby
- # Generate the n-th smooth number that is the product of a given subset of primes.
- # See also:
- # https://en.wikipedia.org/wiki/Regular_number
- # https://en.wikipedia.org/wiki/Smooth_number
- func smooth_generator(primes) {
- var s = primes.len.of { [1] }
- func {
- var n = s.map { .first }.min
- { |i|
- s[i].shift if (s[i][0] == n)
- s[i] << (n * primes[i])
- } * primes.len
- return n
- }
- }
- func nth_smooth_number(n, primes) {
- var g = smooth_generator(primes)
- (n-1).times { g.run }
- g.run
- }
- say nth_smooth_number( 12, [2,7,13,19])
- say nth_smooth_number( 25, [2,5,7,11,13,23,29,31,53,67,71,73,79,89,97,107,113,127,131,137])
- say nth_smooth_number(500, [7,19,29,37,41,47,53,59,61,79,83,89,101,103,109,127,131,137,139,157,167,179,181,199,211,229,233,239,241,251])
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