Created
August 30, 2013 00:57
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prime
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| def is_prime?(number) | |
| if number < 2 || !(number.is_a?(Integer)) | |
| false | |
| else | |
| (2..((number ** 0.5).floor)).all? { |possible| number % possible != 0 } ? true : false | |
| end | |
| end | |
| def prime(number) | |
| if number < 1 || !(number.is_a?(Integer)) | |
| raise TypeError.new "the number given must be an integert greater than zero" | |
| end | |
| primes = [] | |
| potential_prime = 2 | |
| while primes.length < number do | |
| primes << potential_prime if is_prime?(potential_prime) | |
| potential_prime += 1 | |
| end | |
| primes[-1] | |
| end |
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| require 'rspec' | |
| require 'prime' | |
| describe 'is_prime?' do | |
| it 'returns false for ineligible numbers' do | |
| is_prime?(-3).should be_false | |
| is_prime?(0).should be_false | |
| is_prime?(1).should be_false | |
| is_prime?(1.5).should be_false | |
| end | |
| it 'tells if a number is prime or not' do | |
| is_prime?(3).should be_true | |
| is_prime?(6).should be_false | |
| end | |
| end | |
| describe 'prime' do | |
| it 'raises an exception if the input is not an integer greater than 0' do | |
| expect { prime(0) }.to raise_exception | |
| end | |
| it 'returns an nth prime number' do | |
| prime(100).should eq 541 | |
| prime(10_001).should eq 104743 | |
| end | |
| end |
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