正确检查单词是否在字符串中？

def match_string(target, pattern):
    n = len(target)
    m = len(pattern)
    if n < m:
        return False

    # 计算pattern的前缀函数
    prefix = [0] * m
    j = 0
    for i in range(1, m):
        while j > 0 and pattern[i] != pattern[j]:
            j = prefix[j-1]
        if pattern[i] == pattern[j]:
            j += 1
        prefix[i] = j

    # 使用KMP算法进行匹配
    j = 0
    for i in range(n):
        while j > 0 and target[i] != pattern[j]:
            j = prefix[j-1]
        if target[i] == pattern[j]:
            j += 1
        if j == m:
            return True

    return False

target = "hello world"
pattern = "world"
print(match_string(target, pattern))  # True