@Override
    public int hashCode() {
      return patternIndex;
    }
Since the transition generation of one patternNode need to judge based on next patternNode.
Therefore, we implemented this method for previous node.

@return the num of fuzzy transitions of patternNode[patternIndex - 1]
iotdb-core/node-commons/src/main/java/org/apache/iotdb/commons/path/fa/nfa/SimpleNFA.java