Adds a set of methods to classes of Ruby to make them more applicable to algorithmic and mathematical challenges.

hackerrank.rb

class Array
    def prod
        if self.length == 0
            return 0
        end
        z = 1
        self.each do |a_i|
            z *= a_i
        end
        return z
    end
end

class Integer
    def fact
        if self <= 0
            return 0
        end
        z = 1
        (2..self).each do |i|
            z *= i
        end
        return z
    end
    def prime?
        if self < 2
            return false
        end
        if self == 2
            return true
        end
        if self % 2 == 0
            return false
        end
        d_i = 3
        while d_i <= Math.sqrt(self)
            if self % d_i == 0
                return false
            end
            d_i += 2
        end
        return true
    end
end

class Range
    def exclude_begin
        if self.size == 0
            return nil
        end
        if self.exclude_end?
            return ((self.begin + 1)...self.end)
        else
            return ((self.begin + 1)..self.end)
        end
    end
    def exclude_end
        if self.size == 0
            return nil
        end
        return (self.begin...self.end)
    end
    def prod
        if self.size == 0
            return nil
        end
        z = 1
        self.each do |i|
            z *= i
        end
        return z
    end
    def sum
        if self.size == 0
            return nil
        elsif self.size == 1
            return self.begin
        end
        b = self.begin
        e = self.end
        if b.is_a?(Integer) && e.is_a?(Integer)
            e -= 1 if self.exclusive_end?
            n = e - b + 1
            return (b + e) * n / 2
        elsif
            return self.reduce{ |a, b| a + b }
        end
    end
end

class String
    def palindrome?
        if self.size <= 1
            return true
        end
        i, j = 0, self.size-1
        while i < j
            if self[i] != self[j]
                return false
            end
            i, j = i+1, j-1
        end
        return true
    end
end