leecode如何替换空格

示例 1：输入：s = "We are happy."输出："We%20are%20happy."

限制：0 <= s 的长度 <= 10000

class Solution:    def replaceSpace(self, s: str) -> str:        if s is None:            return s        # 转换成列表后再拼接        '''        s_l = s.split(' ')        length = len(s_l)        res = ''        for i in range(length-1):  # 最后一位不加            res += s_l[i] + '%20'        res += s_l[-1]        return res        '''        # 直接遍历的时候遇到空格再添加        res = []        for i in s:            if i == ' ':                res.append('%20')            else:                res.append(i)        return ''.join(res)