remove_duplicates1.rb

def remove_duplicates(nums)
  	i=0

	len= nums.length
	for n in (1..len)

		if (nums[i] == nums[i+1])
			nums.delete_at(i)
		else
			i=i+1
		end
	end

    return nums.length  
end

remove_duplicates2.rb

def remove_duplicates(nums)
    left = 0
    right = 1
    
    while (right < nums.length) do
        nums[left] == nums[right] ? (nums[right] = nil) : (left = right)
        right += 1
    end
    
    nums.compact!
    nums.length
end

remove_duplicates3.rb

def remove_duplicates(nums)
    nums.uniq!
    nums.length
end