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# using first order functions

def factorial(n)
  (1..n).inject(:*) || 1
end

factorial(4)
 => 24

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Prelude> let factorial n = product [1..n]
Prelude> factorial 2
2
Prelude> factorial 3
6
Prelude> factorial 4
24

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punctuation = %w{; = - _ . , ? ! $}
letters = [('a'..'z'), ('A'..'Z')].map { |i| i.to_a }.flatten
"#{punctuation.sample}#{(0...10).map { letters[rand(letters.length)] }.join}#{rand(1000)}"

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# just in case you work in a server were you do not have package groups defined. RHEL / CentOS
# yum groupinstall 'Development Tools'
yum -y install autoconf automake binutils bison flex gcc gcc-c++ gettext libtool make patch pkgconfig redhat-rpm-config rpm-build rpm-sign

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def combinations(array)
  m = array.length
  (1...2**m).map do | n |
    (0...m).select { | i | n[i] == 1 }.map { | i | array[i] }
  end
end

def calculate_combinations(comb_array, target_sum=15)
  combinations(comb_array).map {|a| [a, a.inject(:+)]}.select {|v| v if v.last == target_sum}
end

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a = 95800
b = 217519
c = 414560
d = 422481
a**4 + b**4 + c**4 == d**4 # => true

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# https://codility.com/demo/results/demoKSSE8R-5B3/
# A small frog wants to get to the other side of the road
# two solutions, this one gets 33% of scores:

def solution(x, y, d)
    y % d > 0 ? ((y - x) / d) + 1 : (y - x) / d
end

# this gets 100% scores:
def solution(x, y, d)

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def fibonacci(n)
  n <= 1 ? 1 : fibonacci(n - 1) + fibonacci(n - 2)
end

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Initial solution, test passing, 0% scores:

(1..a.size-2).each {|i| p (a.slice(i,a.size).inject(:+) - a.slice(0, i).inject(:+)) }.min

I found this on internet, 100% scores, very long:

    puts "tape_equilibrium: "
    return 0 if a.empty?
    # Example data: N=5, P(1-4), A[3,1,2,4,3]
    # P1:

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(1..100).each {|i| print i; print  ' fizz' if i%3 == 0; print ' buzz' if i%5 ==0; puts}

# recursive
def fizzbuzz(n = 1)
  if n < 101
    print "#{i}: "
    print "Fizz" if 0 == i % 3
    print "Buzz" if 0 == i % 5
    print "\n"
    fizzbuzz(n + 1)