def _longest_common_substring_length(a, b):
    if not a or not b:
        return 0

    prev = [0] * (len(b) + 1)
    max_len = 0
    for i in range(1, len(a) + 1):
        curr = [0] * (len(b) + 1)
        for j in range(1, len(b) + 1):
            if a[i - 1] == b[j - 1]:
                curr[j] = prev[j - 1] + 1
                if curr[j] > max_len:
                    max_len = curr[j]
        prev = curr
    return max_len


def analyze_fields(question, field_list):
    if question is None or field_list is None:
        return {}

    fields = field_list.split("@@")
    ratios = []
    field_count = 0

    for field in fields:
        if not field:
            continue
        field_count += 1
        lcs_len = _longest_common_substring_length(question, field)
        ratios.append(lcs_len / len(field))

    if field_count == 0:
        return {}

    non_zero = sum(1 for r in ratios if r != 0)
    avg = sum(ratios) / field_count
    max_ratio = max(ratios) if ratios else 0

    return {
        "field_count": field_count,
        "non_zero_count": non_zero,
        "avg_ratio": avg,
        "max_ratio": max_ratio,
    }