Simulate robot on grid with obstacles

A robot starts at (0, 0) on an unbounded integer grid. You are given a sequence of commands consisting of characters U, D, L, and R, and a set of blocked cells (obstacles). For each command, the robot attempts to move one cell in the indicated direction; if the destination cell is blocked, it does not move for that command and proceeds to the next. Return the maximum squared Euclidean distance from the origin reached at any time during the simulation. Design an algorithm that handles up to 1e5 commands and 1e5 obstacles efficiently; describe data structures (e.g., hash set for obstacles), complexity, and edge cases.