问对替换空格的python代码的时间复杂度有更严格的限制

EN

def URLify(string, length):
    string = list(string)
    j = length - 1
    i = j - 1
    while i > 0:
        if string[i - 1] == " ":
            for k in range(j, i - 1, -1):
                string[k + 2] = string[k]

            string[i] = "2"
            string[i + 1] = "0"
            string[i - 1] = "%"
            j = j + 2

        i = i - 1

    return "".join(string)


string = "Mr John Smith       "
length = 13
print(URLify(string, length))
##Output:  Mr%20John%20Smith