Problem context and objectives
Mission briefing
Game event engineer · Actions arrive faster than the world can resolve them
Process events in the exact order promised by the data structure: The Prefix Rescue.
The wrong removal order changes gameplay and creates impossible replays.
How you win
- 1Recognize when Increasing prefix deque matches the clues
- 2Keep this true after every move: deque prefix sums increase and their indices are the only undominated starts
- 3Reach the result within O(n)
Rules and pressure
- Target cost: O(n)
- State rule: deque prefix sums increase and their indices are the only undominated starts
New words in this mission
Open a term for a plain-language explanation.invariant+
A statement that must remain true after every meaningful step. It is the safety rule connecting the visual state to correct code.
Lesson 1 of 3
Negative values break an ordinary sliding window. Prefix differences preserve exact sums: the front yields valid spans while the back keeps only undominated starts.
Your call · Prefix 3 minus front prefix 0 is 3. What next?