[LeetCode] 093. Restore IP Addresses

# Backtracking
class Solution1:
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        res = []
        self.backtrack(res, [], s)
        return res

    def backtrack(self, res, item, s):
        if len(item) == 4:
            if len(s):
                return
            else:
                res.append('.'.join(item))
                return

        if len(s) > 0:
            self.backtrack(res, item + [s[:1]], s[1:])
        if len(s) > 1 and int(s[:2]) > 9:
            self.backtrack(res, item + [s[:2]], s[2:])
        if len(s) > 2 and 99 < int(s[:3]) < 256:
            self.backtrack(res, item + [s[:3]], s[3:])