Stack problem once you see it, but I didn't see it right away.
Use a stack to simulate collisions by iterating through the asteroids. For each asteroid, if it moves right, push it; if it moves left, resolve collisions with the stack top until it is destroyed or the stack is empty or the top moves left. Finally, the stack contains the surviving asteroids.
Pro tip: Clarify the collision rules upfront and walk through a small example to demonstrate your understanding. Emphasize that only right-moving asteroids followed by left-moving ones can collide, and handle edge cases like all asteroids moving in the same direction.
Restate the problem to ensure clarity: asteroids move in a row, signs indicate direction, magnitudes indicate size. Collisions occur only between a right-moving asteroid and a left-moving asteroid that are adjacent after previous collisions.
Select a stack to efficiently manage asteroids and resolve collisions. The stack will store asteroids that are moving right or have survived collisions.
Traverse the array. For each asteroid, if it moves right, push onto stack. If it moves left, repeatedly compare with the top of the stack: if top is positive (right-moving), resolve collision based on sizes; if top is negative or stack empty, push the left-moving asteroid.
When a right-moving asteroid (top) and left-moving asteroid (current) collide: if top is smaller, pop and continue comparing; if equal, pop and discard current; if top is larger, discard current. If current survives all comparisons, push it.
After processing all asteroids, the stack contains the final state. Convert the stack to an array and return it.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.