Strings

[mat65]

x1, x2 are two strings. you should find what is the length of the largest substring of x2 containing only letters from x1. For example: if x1="abc" and x2="cvbaacdab" the answer will be 4 because "baac" is the largest substring.
can you help me find a recursive way (no loops please) to find the answer?

[Londbrok]

Sound like a school assignment, to get help on those, much better to show some effort, ask specific questions on whatever issues you are stuck with.

Just posting the assignment, does not really give anything to help or comment on, does it? So be more specific, on what you are having difficulty with, recursion, String comparison or what?

[mat65]

it is not an assignment but a trial to teach myself java.
I found this question but didn't find the answer.. I know how to find the longest substring if it starts at the end of x2 using indexOf and charAt and substring but don't find a way to do it if it somewhere else.

[_uj]

x1, x2 are two strings. you should find what is the length of the largest substring of x2 containing only letters from x1. For example: if x1="abc" and x2="cvbaacdab" the answer will be 4 because "baac" is the largest substring.
can you help me find a recursive way (no loops please) to find the answer?

It's quite easy to turn iteration into recursion. Instead of returning to the beginning of a loop for another iteration, the recursive method calls itself, like

void loop(int N) { // iteration
   for (int i=0; i<N; i++) {
      // do
   }
}
//
void rec(int i, int N) { // equivalent recursion
   if (i<N) {
      // do
      rec(i+1, N); // next "iteration"
   }
}

So if you have an iterative solution strategy ready, its quite straightforward to turn it into recursion.

The above is called "tail" recursion and isn't very elegant. If you want to secure an A you should use a divide-and-conquer approach instead.