原题地址：https://oj.leetcode.com/problems/restore-ip-addresses/

题意：

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

For example:

Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

解题思路：这个明显是用dfs来解决。来一段精致简练的代码吧。

代码：

class Solution:    # @param s, a string    # @return a list of strings    def restoreIpAddresses(self, s):        def dfs(s, sub, ips, ip):            if sub == 4:                                        # should be 4 parts                if s == '':                    ips.append(ip[1:])                          # remove first '.'                return            for i in range(1, 4):                               # the three ifs' order cannot be changed!                if i <= len(s):                                 # if i > len(s), s[:i] will make false!!!!                    if int(s[:i]) <= 255:                        dfs(s[i:], sub+1, ips, ip+'.'+s[:i])                    if s[0] == '0': break                       # make sure that res just can be '0.0.0.0' and remove like '00'        ips = []        dfs(s, 0, ips, '')        return ips