Maze Runner

MetaOnsiteMedium

You are given a maze as a list of equal-length strings, one per row. S marks the start and E the exit, and each appears exactly once. # is a wall that cannot be entered and . is open floor. Each move goes one cell up, down, left or right and costs 1 step.

Implement shortest_path(grid), which returns the fewest steps needed to walk from S to E, or -1 if E cannot be reached. The parts below add rules to the maze one at a time.

Part 1: Shortest path

Find the fewest steps from S to E, moving between orthogonally adjacent open cells. In this part the grid contains only S, E, # and .. Return -1 if E cannot be reached.

Example 1
grid
["S..#","#.#.","...E"]
Output
5
Why: The only route goes right once, down twice, then right twice into E: 5 steps; the walls leave nothing shorter.

Constraints

1 <= len(grid) <= 50
1 <= len(grid[i]) <= 50
grid[i][j] is one of S, E, #, .