code: public boolean isMatch(int count) {
          if (a == 0) {
              return count == b;
          } else if (a > 0) {
              if (count < b) {
                  return false;
              }
  
              return (count - b) % a == 0;
          } else {
              if (count > b) {
                  return false;
              }
  
              return (b - count) % (-a) == 0;
          }
      }
docs: Check if the <em>node</em> count matches this specifier.
  
  @param count The <em>node</em> count.
  @return <code>true</code> or <code>false</code>.