algorithm - subset sum from recursive backtracking -

i trying modify "list combinations in string" question, problem need print sets have given 'sum'. here initial code, not sure how can save list of sets in code:

/**  * method return  sets given sum.  **/ public static list<list<integer>> lists = new arraylist<>(); public static list<integer> list = new arraylist<integer>(); public static void countsubsetsum3(int arr[], int k, int sum) {     if(sum == 0) {         return;     }     if(sum != 0 && k == 0) {         return;     }     if(sum < arr[k - 1]) {         countsubsetsum3(arr, k-1, sum);     }     countsubsetsum3(arr, k-1, sum - arr[k-1]);     countsubsetsum3(arr, k-1, sum); } 

how can modify code make print possible sets have sum 'sum'. thanks!

you have return function when string's length 0. right you're printing prefix , line:

subset(prefix + string.charat(0), string.substring(1)); 

is executed, raises stringindexoutofboundsexception because you're calling .substring(1) on empty string.