Asteroid collision

Given an array of integers representing asteroids in a row, the absolute value is each asteroid's size and the sign is its direction (positive = moving right, negative = moving left). All asteroids move at the same speed. When two asteroids collide, the smaller one explodes; if both are equal, both explode. Two asteroids moving in the same direction, or a left-mover to the left of a right-mover, never meet. Return the state of the asteroids after all collisions resolve.