Programming Exercises



Write a method that takes a string and returns the number of unique characters in the string. It is expected that a string with the same character sequence may be passed several times to the method. Since the counting operation can be time consuming, the method should cache the results, so that when the method is given a string previously encountered, it will simply retrieve the stored result. Use collections and maps where appropriate.


Write a program which creates a concordance of characters occurring in a string (i.e., which characters occur where in a string). Read the string from the command line.

Running the program:

>java Concordance Hello World
{d=[9], o=[4, 6], r=[7], W=[5], H=[0], l=[2, 3, 8], e=[1]}