Asteroid Collision
Find state of asteroids after all collisions Positive = moving right, Negative = moving left When asteroids collide: smaller explodes, equal = both explode Asteroids moving same direction never meet Example: [5,10,-5] => [5,10] (10 destroys -5)
This is a stack/invariant problem: once your stack represents the right thing, the rest is routine. Interviewers love it because it reveals your stack invariants and your edge-case discipline. The classic mistake is not being clear about what your stack represents at each step.
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