/**  *  get combinations ( C(superscript, subscript) )  * @param totalCount  normal data node group count except primary data node group * @param selectCount secondary data node count * @return the possibility of combinations * e.g. the possibility of select 2 members from 5 members * the possibility: {[5,4], [5,3], [5,2], [5,1], [4,3], [4,2], [4,1], [3,2], [3,1], [2,1]} */ private List
    
     
      > getCombination(int totalCount, int selectCount){ //The combination of secondary count from group Count which expect primary group . int comb[] = new int[selectCount+1]; comb[0] = selectCount; List
      
       
        > resultIndexList = new ArrayList<>(); combination(comb, totalCount, selectCount, resultIndexList); logger.info("secondary group index combination:{}", resultIndexList); return resultIndexList; } /** * get combinations( C(superscript, subscript) ) * e.g. C(5, 2) ,the resultList: {[5,4], [5,3], [5,2], [5,1], [4,3], [4,2], [4,1], [3,2], [3,1], [2,1]} * @param comb last result of combination * @param superscript max of the number * @param subscript select numbers count * @param resultList result after combination */ private void combination(int comb[], int superscript, int subscript, List
        
         
          > resultList) { for (int i = superscript; i >= subscript; i--) { // select current head element comb[subscript] = i; if (subscript > 1) { // enter next smaller combination combination(comb, i-1, subscript-1, resultList); } else { Deque
          
            selectIndexQueue = new ArrayDeque<>(); // save combination for (int j=comb[0]; j>0; j--) { selectIndexQueue.add(comb[j]); } resultList.add(selectIndexQueue); } } return; }