如何在不使用多个循环的情况下检查单词是否在字符串中

def build_next(pattern):
    """
    构建模式串的next数组
    """
    next = [0] * len(pattern)
    j = 0
    for i in range(1, len(pattern)):
        while j > 0 and pattern[i] != pattern[j]:
            j = next[j-1]
        if pattern[i] == pattern[j]:
            j += 1
        next[i] = j
    return next

def kmp_search(text, pattern):
    """
    使用KMP算法在字符串中检查单词是否存在
    """
    next = build_next(pattern)
    i, j = 0, 0
    while i < len(text) and j < len(pattern):
        if text[i] == pattern[j]:
            i += 1
            j += 1
        elif j > 0:
            j = next[j-1]
        else:
            i += 1
    if j == len(pattern):
        return True
    return False

# 示例用法
text = "This is a sample text."
pattern = "sample"
result = kmp_search(text, pattern)
print(result)  # 输出：True