Assignment #5: More Recursion

Basic problem

A non-contiguous substring of String s is a sequence of k >= 0 characters in s, in the order in which they occur in s. For instance, the following table shows ALL the non-contiguous substrings of some String s.

String s        All non-contiguous substrings of s
========        ==================================
""              ""
"a"             "" "a"
"ab"            "" "a" "b" "ab"
"abc"           "" "a" "b" "ab" "c" "ac" "bc" "abc"

Write a routine generateAll that returns an ArrayList containing all the non-contiguous substrings of parameter s, and test it.