I see that the command that you are using has only input path where your data set is present and an output path but you have not mentioned your package name along with the class name. So, It was unable to locate the class.
The command is as below for executing map reduce codes:
hadoop jar wc.jar practice.word_count wordcountproblem /user/hduser/wc_mr
Where wc.jar is the name of the jar that you export from eclipse, practice is the name of the package in which we have the class, this can differ if you have a different class name, word_count is the class name in which you have the code for word counting, wordcountproblem is the data set that you have transferred to hdfs. This may change depending on the exact path of your data set in the hdfs.