code: def _longest_common_prefix_length(
      s1: np.ndarray,
      s2: np.ndarray,
      previous_best: Optional[float] = None,
  ) -> float:
      """Compute the length of the longest common prefix."""
      min_len = min(len(s1), len(s2))
      s1, s2 = s1[:min_len], s2[:min_len]
      (nonzeros,) = np.cumprod(
          s1 == s2
      ).nonzero()  # Get indices (inclusive) up to which s1 and s2 are the same.
      result = np.max(nonzeros) + 1 if len(nonzeros) > 0 else 0
      return (
          result
          if previous_best is None
          else max(previous_best, result)
      )
  
imports: import re
  from typing import List, Optional
  import numba
  import numpy
  from nltk.tokenize.treebank import TreebankWordTokenizer
  from helm.benchmark.adaptation.request_state import RequestState
  from helm.benchmark.adaptation.adapter_spec import AdapterSpec
  from helm.benchmark.scenarios.scenario import Reference
  from helm.common.request import RequestResult
  from .metric import Metric
  from .metric_name import MetricName
  from .metric_service import MetricService
  from .statistic import Stat
label_desc: Use image node_id 1 for calling a global function with example usage: _longest_common_prefix_length(s1, s2, previous_best) and returns: unknown