comefrom: <awangdev>Combinations_2.java
code: public void helper(List<List<Integer>> rst, 
                  List<Integer> solution, int n, int k, int start) {
          if (solution.size() == k) {
              rst.add(new ArrayList(solution));
              return;
          }        
          for (int i = start; i <= n; i++) {
              solution.add(i);
              helper(rst, solution, n, k, i + 1);
              solution.remove(solution.size() - 1); 
          }
      }
masked: public void sample_funcname ( List < List < Integer >> rst , List < Integer > solution , int n , int k , int start ) {
    if ( solution . size ( ) == k ) {
      rst . add ( new ArrayList ( solution ) ) ;
      return ;
    }
    for ( int i = start ;
    i <= n ;
    i ++ ) {
      solution . add ( i ) ;
      helper ( rst , solution , n , k , i + 1 ) ;
      solution . remove ( solution . size ( ) - 1 ) ;
    }
  }
  