Maze Solver: Shortest Path With Keys and Doors (Stateful BFS)

Problem: Shortest Path in a Maze with Keys and Doors You are given an R x C maze: #: wall S: start E: exit .: open cell a-f: keys A-F: doors (door A can be passed only if you have key a) Move 4-directionally; each move costs 1. Return the minimum number of steps from S to E, or -1 if unreachable. Input First line: R C Next R lines: strings of length C Output Minimum steps or -1 Constraints 1 <= R, C <= 200 At most 6 distinct key types (a-f) Note You may need to revisit a cell after picking up a key, so the visited state cannot be just (r, c). Example Input 3 4 S.a# ##A. ...E Output -1