One twitter comment points out that this was the last free-response question on the exam, and that a preceding question was harder than usual. So examinees probably wasted too much time on the earlier question and lacked time to finish the last question. It doesn’t mean the last question was particularly hard.

(The twitter comment: https://twitter.com/m_litv/status/1670144278708748292)

Also, the problem should state whether the candy grid is stored row-major or column-major: is it `box[row][column]` or `box[column][row]`? As far as I can tell, that detail isn’t specified.