无重复字符的最长子串

def solve():
    s = '____'
    char_set = set()
    left = ____
    max_len = ____
    for right in range(len(____)):
        while s[right] in char_set:
            char_set.remove(____)
            left += ____
        char_set.add(____)
        max_len = max(____)
    print(____)