The phrase "a challenging problem and" is correct and usable in written English.
It can be used when discussing a difficult issue or task, often leading into further explanation or additional points.
Example: "The project presents a challenging problem and requires innovative solutions to overcome the obstacles we face."
Alternatives: "a difficult issue and" or "a tough challenge and".
"This is a challenging problem, and something we're thinking deeply about in terms of how we can do a better job.
It is well-known that MO-VRPTW is a challenging problem and has very few Pareto optimal solutions.
It should be noticed that the pinning control design for feedback stabilization of constrained BCNs is still a challenging problem, and there are fewer results on this problem.
These methods play an extremely important role in the development of integer programming, however, it remains a challenging problem and appeals for more endeavors.
Exact simulation from a surface is a challenging problem and general methods are difficult to apply for complicated contours like our star-shaped regions.
Although several popular methods have been developed for integer programming in the literature and extensively utilized in practices, it remains a challenging problem and appeals for more endeavors.
Accurate assignment of secondary structure of proteins from coordinate data is an important and a challenging problem (Andersen and Rost, 2009).
These nosebleeds often cause significant parental concerns and remain a challenging problem to patients and physicians alike [ 1, 2].
For entrepreneurs and innovators, excess capacity provides a challenging problem to solve and an opportunity to be had.
The large amount of factual findings poses a challenging problem for analysis, and even possible quantitative correlation, between particle properties and fluidization behavior.
Predicting and proper ranking of canonical splice sites (SSs) is a challenging problem in bioinformatics and machine learning communities.
