On an alphabet board, we start at position (0, 0), corresponding to character board[0][0]. Here, board = [ "abcde ", "fghij ", "klmno ", "pqrst ", "uvwxy ", "z "], as shown in the diagram below. We may make the following moves: 'U' moves our position up one row, if the position exists on the board; 'D' moves our position down one row, if the position exists on the board; 'L' moves our position left one column, if the position exists on the board; 'R' moves our position right one column, if the position exists on the board; '!' adds the character board[r][c] at our current position (r, c) to the answer. (Here, the only positions that exist on the board are positions with letters on them.