Leetcode 1824. Minimum Sideway Jumps

Given a 3-lane road with obstacles (at most one per position) and a frog starting at lane 2 point 0, find the minimum number of side jumps required to reach point n, where the frog can move forward on the same lane if the next point is free or perform a side jump at the same point to any other non-blocked lane (cost 1). With n up to 5×10^5, this requires an efficient linear-time scan over the three-lane state at each position.