restore ip addresses

class (object):
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        if len(s) > 12 or len(s) < 4:
            return []
        
        res = []
        self.dfs(s, 0, [], res)
        return res
    
    def dfs(self, s, pos, cur, res):
        if pos >= len(s):
            if len(cur) == 4:
                res.append(".".join(cur))
            return
        
        if s[pos] == "0": 
            cur.append(s[pos])
            self.dfs(s, pos + 1, cur, res)
            cur.pop()
        else:
            for i in range(1, 4):
                if pos + i <= len(s) and 0 <= int(s[pos:pos + i]) <= 255:
                    cur.append(s[pos:pos + i])
                    self.dfs(s, pos + i, cur, res)
                    cur.pop()