Method dfs

java/0130-surrounded-regions.java:27–39

(char[][] board, int r, int c)

    }

    private void dfs(char[][] board, int r, int c) {
        int nRows = board.length;
        int nCols = board[0].length;
        if (
            r < 0 || c < 0 || r >= nRows || c >= nCols || board[r][c] != 'O'
        ) return;

        board[r][c] = 'T';
        dfs(board, r + 1, c);
        dfs(board, r - 1, c);
        dfs(board, r, c + 1);
        dfs(board, r, c - 1);
    }
}