Refactoring into java 8 lambda/stream -

when solve subset sum problem or "p = np" takes 5 minutes following code. curious know how faster if using .parallelstream. don't understand how convert code.

public class mainactivity { final static integer[] pops = {8897109, 12828837, 9461105, 6371773, 5965343, 5946800, 5582170, 5564635, 5268860, 4552402, 4335391, 4296250, 4224851, 4192887, 3439809, 3279833, 3095313, 2812896, 2783243, 2710489, 2543482, 2356285, 2226009, 2149127, 2142508, 2134411}; final static int total = 100000000; /**  * @param args  */ public static void main(string[] args) {     combinations c = new combinations(pops, total);     c.chooser(); } 

}

import java.util.arraylist; import org.paukov.combinatorics.factory; import org.paukov.combinatorics.generator; import org.paukov.combinatorics.icombinatoricsvector;   public class combinations { private integer[] pops; private int total;  public combinations(integer[] pops, int total){     this.pops = pops;     this.total = total; }  public void chooser(){     for(int = 1; i<=pops.length; i++){         system.out.println(i);         icombinatoricsvector<integer> initialvector = factory.createvector(pops);         generator<integer> gen = factory.createsimplecombinationgenerator(initialvector, i);         (icombinatoricsvector<integer> combination : gen) {             string temp = combination.tostring();             int size = temp.indexof("size");             temp = temp.substring(22, size-3);             int sum = adder(temp);             if (sum == total){                 system.out.println(temp);             }         }     } }  public int adder(string combos){     int total = 0;     string[] parts = combos.split(", ");     arraylist<integer> nums = new arraylist<>();     for(int = 0; i<parts.length; i++){         nums.add(integer.parseint(parts[i]));     }     for(int temp : nums){         total += temp;     }      return total; } } 

here code string stuff taken out. takes 15 seconds now. realize .parallelstream() not reduce time much, still @ least give me hints on how it.

import java.util.arraylist; import java.util.list;  import org.paukov.combinatorics.factory; import org.paukov.combinatorics.generator; import org.paukov.combinatorics.icombinatoricsvector;   public class combinations { private integer[] pops; private int total;  public combinations(integer[] pops, int total){     this.pops = pops;     this.total = total; }  public void chooser(){     for(int = 1; i<=pops.length; i++){         system.out.println(i);         icombinatoricsvector<integer> initialvector = factory.createvector(pops);         generator<integer> gen = factory.createsimplecombinationgenerator(initialvector, i);         (icombinatoricsvector<integer> combination : gen) {             list<integer> temp = combination.getvector();             int sum = adder(temp);             if (sum == total){                 system.out.println(temp);             }         }     } }  public int adder(list<integer> combos){     int total = 0;     for(integer temp : combos){         total+=temp;     }     return total; } } 

this runs 3 times fast on box (i7-2600 hyper-threading, 8 virtual cores):

public class combinations {     private integer[] pops;     private int total;      public combinations(integer[] pops, int total) {         this.pops = pops;         this.total = total;     }      public void chooser() {         icombinatoricsvector<integer> initialvector = factory.createvector(pops);          intstream.range(1, pops.length + 1).parallel()                 .peek(system.out::println)                 .maptoobj(i -> factory.createsimplecombinationgenerator(initialvector, i))                 .flatmap(gen -> gentostream(gen, false)                         .map(icombinatoricsvector::getvector)                         .filter(v -> adder(v) == total))                 .foreach(system.out::println);     }      public static int adder(iterable<integer> combos) {         int total = 0;         (integer temp : combos) {             total += temp;         }         return total;     }      public static <e> stream<icombinatoricsvector<e>> gentostream(generator<e> gen, boolean parallel) {         return streamsupport.stream(spliterators.spliterator(gen.iterator(),                 gen.getnumberofgeneratedobjects(), spliterator.ordered), parallel);     } } 

this uses parallel stream outer loop, regular stream inner loop, , avoids using stream sum list (for speed). can try parallel inner stream gentostream(gen, true), didn't see difference in speed.

also, if want list<list<integer>> of matches, change foreach line .collect(collectors.tolist());.