题解 | 数字字符串转化成IP地址

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param s string字符串 
# @return string字符串一维数组
#
class Solution:
    def restoreIpAddresses(self , s: str) -> List[str]:
        # write code here
        if len(s)>12:
            return []
        res, path = [], []
        def dfs(index):
            if index > len(s):
                return
            if index == len(s) and len(path) == 4:
                res.append(".".join(path[:]))
                return
            for i in range(index, len(s)):
                if 0 <= int(s[index:i+1]) <=255:
                    if s[index] == "0" and len(s[index:i+1]) > 1:
                        continue
                    path.append(s[index:i+1])
                    dfs(i+1)
                    path.pop()
        dfs(0)
        return res