three_sum.rb

def three_sum(nums)
  res = []
  nums.sort!
  (0...nums.length - 2).each do |i|
    next if i > 0 && nums[i] == nums[i + 1]
    l = i + 1
    r = nums.length - 1
    while l < r
      s = nums[i] + nums[l] + nums[r]
      if s > 0
        r -= 1
      elsif s < 0
        l += 1
      else
        res.push([nums[i], nums[l], nums[r]])

        l += 1 while l < r && nums[l] == nums[l + 1]
        r -= 1 while l < r && nums[r] == nums[r - 1]
        l += 1
        r -= 1
      end

    end
  end
  res
end

x = [-1, 0, 1, 2, -1, -4]

print 'input: '
p x
print 'output should be: '
p [[-1, -1, 2], [-1, 0, 1]]
print 'output: '
p three_sum(x)