写个最长无重复子串吧~

def length_of_longest_substring(st):
    max_length = 0
    max_substring = ""
    if not st:
        return 0, ""
    i, j = 0, 0
    while j < len(st):
        if st[j] not in st[i:j]:
            j += 1
            if j == len(st):
                if max_length < j - i:
                    max_length = j - i
                    max_substring = st[i:j]
        else:
            if max_length < j - i:
                max_length = j - i
                max_substring = st[i:j]
            i += 1
    return max_length, max_substring

# 测试通过
str1 = ""
str2 = "a"
str3 = "ab"
str4 = "abc"
str5 = "abbcdefgdhf"
for st in [str1, str2, str3, str4, str5]:
    print(length_of_longest_substring(st))
    

空间消耗太多