leetcode 93. Restore IP Addresses

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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)

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class Solution(object):
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        ans = []
        self.dfs(ans,s,4,[])
        return ['.'.join(x) for x in ans]
    def dfs(self,ans,s,k,temp):
        if len(s) > 3*k:
            return []
        if k == 0:
            ans.append(temp[:])
        else:
            for i in range(min(3,len(s)-k+1)):
                if i == 2 and int(s[:3]) > 255 or i > 0 and int(s[0]) == 0:
                    continue
                self.dfs(ans,s[i+1:],k-1,temp+[s[:i+1]])