The last line of the input file in the example reflects that the right limit of the black interval is 47. But the white interval in the output file begins with 47. How can it be??

If one supposes that limits of these intervals are not included then they are shouldn't be included in the 3rd and the 4th lines either. Then the white interval ends with 299 and another one begins with 301. But the answer would be "301 633" this way.

What is the right way to understand the terms of this problem?

It's the axis we are painting, therefore you have to think continuous interval . I think if the range is 1 2, then all to left of 2 up to 1 is painted, and all to right is unchanged.