Grid Navigator with Teleporters

You are given a 2D grid of characters representing a maze. The grid can contain the following characters:

• S: The starting point. There will be exactly one starting point.
• E: The ending point. There will be exactly one ending point.
• .: An open cell through which you can walk.
• #: An obstacle that you cannot pass through.
• Uppercase letters (A-Z): Teleporter cells. Each letter appears exactly twice in the grid. If you step onto one teleporter, you can instantly move to the other cell with the same letter without using an extra step. Teleportation using a letter is optional.

You can move in the four cardinal directions (up, down, left, right), and moving to an adjacent open cell counts as 1 step. Your task is to find the minimum number of steps to reach the ending point E from the starting point S. If it is impossible to reach E, return -1.

Input Format

• A 2D grid represented as a list of strings (or equivalent in your language), where each string represents a row of the maze.

Output Format

• An integer representing the minimum number of steps required to reach E from S, or -1 if it is not possible.

Example

Consider the following grid:

S.A..
.##.#
..#A.
.##E.

• The starting position is at (0, 0) and the ending position is at (3, 3) (assuming 0-based indexing).
• There are obstacles (#) that block movement.
• There is a pair of teleporters labeled A at positions (0, 2) and (2, 3). When you step onto one of these, you can instantly teleport to the other cell with no additional cost.

Based on this grid, your function should determine the minimum number of steps from S to E.

Constraints

• The dimensions of the grid (rows and columns) will be at least 2 and at most 100.
• It is guaranteed that there is exactly one S and one E in the grid.
• Each uppercase letter used as a teleporter appears exactly twice.

Write a function or method in your preferred programming language to solve the problem as described.