code: private boolean hasCandidate(int n) {
          for (int j = (n * matrix.mCols), end = (j + matrix.mCols); j < end; j++)
              if (matrix.get(j)) return true;
          return false;
      }
docs: Check if there are any feasible mappings left for the query vertex n. We
  scan the compatibility matrix to see if any value is > 0.
  
  @param n query vertex
  @return a candidate is present