I am getting an error about uncheched or unsafe operations

#1

Note: Main.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

What is this error and how to solve it.

#2

hey @HimanshuSingh8998
line 25 : ArrayList mr = new ArrayList<>(); instead of ArrayList mr = new ArrayList()
Same here ArrayList ab = new ArrayList();