打卡群刷题总结0803——复原IP地址

class Solution(object):
    # 判断是否有效
    def isValid(self, s):
        if len(s) >1 and s[0] == '0':
            return False
        if 0 <= int(s) <= 255:
            return True
        return False
    
    def split(self, s, start, num, current):
        # 数字长度是否满足要求
        if len(s) - start < num or len(s) - start > 3 * num:
            return 
        # 只有一位时，判断是否有效
        if num == 1:
            if self.isValid(s[start:]):
                current2 = copy.copy(current)
                current2.append(s[start:])
                self.res.append('.'.join(current2))
            return
        # 其他情况，split
        for i in range(start + 1, len(s) - num + 2):
            if self.isValid(s[start: i]):
                current2 = copy.copy(current)
                current2.append(s[start: i])
                self.split(s, i, num - 1, current2)
            else:
                break
        
    def restoreIpAddresses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        self.res = []
        self.split(s, 0, 4, [])
        return self.res