Subtask strategy

Questions 1 to 5 of 8

1. 1. Staircase Permutation asks for a permutation of 1 to n where every two neighbours differ by at least 2, or -1 if none exists. What is the correct output for n = 3?

   2 3 11 3 23 1 2-1
2. 2. An AI tool wrote a Staircase Permutation solver. Its output matches the sample for n = 4, but the judge gives WA on the largest subtask. The judge accepts any valid answer. Which check would have caught the bug?

   A validator that checks every neighbour pair of the output and runs for the largest n tooComparing the output with the sample output line by lineRunning the solver once more on the same inputReading the code to see whether it uses sorting
3. 3. Which two statements about checkers for many-answer problems are true?

   Pick every answer that is true.

   A checker reads the input and your output, and decides whether the output is validA checker compares your output with one fixed answer, so only one output can passFor small n, a checker can search for a valid answer with a method that does not share the solver's ideaThe checker should be built from the same idea as the solver, so that the two always agree
4. 4. The lesson's plan for a 150-minute set gives steps 2 to 5 (the cheap subtasks) a total of how many minutes of writing, for 150 points?

   Type a number.

5. 5. Under the 150-minute plan, the Range Order full solution (70 points, about 45 minutes) is step 6, after the cheap steps. Why does the lesson put it there?

   Because it is worth the fewest points of the four problemsBecause it is the longest step and may not finish, so a late finish does not cost the easy pointsBecause a judge reads only the first subtask submittedBecause every subtask 1 program must be finished before any full solution is started