字符串的最大无重复子串

1. 关键思想：滑动窗口
2. 代码：

def solve(s):
    l = len(s)
    if not s:
        return 0
    if l == 1:
        return 1
    begin = 0
    end = begin
    str_map = set()
    maxlen = 0
    while end < len(s):
        if s[end] not in str_map:
            str_map.add(s[end])
            end += 1
            if len(str_map) > maxlen:
                maxlen = len(str_map)
        else:
            begin += 1
            end = begin
            str_map = set()