使用 Array 方法的素数列表 [英] List of prime numbers using Array methods
问题描述
我有一个代码来获取质数列表:
I have a code to get list of prime numbers:
def primes_numbers num
primes = [2]
3.step(Math.sqrt(num) + 1, 2) do |i|
is_prime = true
primes.each do |p| # (here)
if (p > Math.sqrt(i) + 1)
break
end
if (i % p == 0)
is_prime = false
break
end
end
if is_prime
primes << i
end
end
primes
end
是否可以使用数组方法(选择、收集等...)重写代码?类似的东西:
Is it possible rewrite code using Array methods (select, collect and so on...)? Something like:
s = (3..n)
s.select { |x| x % 2 == 1}.select{ |x| ..... }
问题是我需要在 select 方法中遍历结果数组(注释此处").
The problem is that I need to iterate throught result array (comment 'here') in the select method.
推荐答案
Ruby 1.9 有一个非常好的 Prime
类:
Ruby 1.9 has a very nice Prime
class:
http://www.ruby-doc.org/core-1.9/classes/Prime.html
但我假设您不关心任何标准类,但想查看一些代码,所以我们开始:
But I'm assuming you don't care about any standard classes, but want to see some code, so here we go:
>> n = 100 #=> 100
>> s = (2..n) #=> 2..100
>> s.select { |num| (2..Math.sqrt(num)).none? { |d| (num % d).zero? }}
#=> [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]
注意:我这样写是因为你想要 Enumerable 方法,为了效率起见,你可能想阅读主要的查找方法.
Note: I wrote it this way because you wanted Enumerable methods, for efficiency's sake you probably want to read up on prime finding methods.
这篇关于使用 Array 方法的素数列表的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!