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: Echo Cancellation.
The wrong removal order changes gameplay and creates impossible replays.
How you win
- 1Recognize when Stack cancellation matches the clues
- 2Keep this true after every move: the stack is the fully reduced form of the processed prefix
- 3Reach the result within O(n)
Rules and pressure
- Target cost: O(n)
- State rule: the stack is the fully reduced form of the processed prefix
Lesson 1 of 3
Each incoming echo collides only with the stack top. A match dissolves both; a mismatch locks the new echo into the unresolved stack.
Your call · When reading the second b in abb, what happens?