You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
14 lines
334 B
Ruby
14 lines
334 B
Ruby
# Count the number of prime numbers less than a non-negative number, n.
|
|
#
|
|
# @param {Integer} number
|
|
# @return {Integer}
|
|
|
|
def count_primes(n)
|
|
primes = [nil, nil, *2..n]
|
|
(0..Math.sqrt(n)).each do |i|
|
|
(i**2..n).step(i) { |composite_number| primes[composite_number] = nil } unless primes[i].nil?
|
|
end
|
|
|
|
primes.compact.count
|
|
end
|