They also apply to a specified travel window. This month sees enticing offers for one-way economy flights between select U.S. cities and Europe starting at 18,750 miles. Plus, two routes between ...

return [nums[i:i+3] for i in xrange(0, len(nums), 3)] if all(nums[i+2]-nums[i] <= k for i in xrange(0, len(nums), 3)) else [] ...