Parse a password from a matrix

Given an m x n matrix of characters, a starting coordinate (row, col), and a string of moves consisting of 'U', 'D', 'L', 'R', parse a password by visiting cells in order: append the character at each visited cell unless it is the same as the previous appended character. Cells marked '#' are blocked and cannot be entered. If a move would leave the grid or hit a blocked cell, return an error. Return the final password string and analyze time/space complexity.