代码随想录算法训练营第二十八天| 93.复原IP地址、78.子集、90.子集II

93.复原IP地址

题目链接：力扣（LeetCode）官网 - 全球极客挚爱的技术成长平台

解题思路：

java：

class Solution {
    List<String> result = new ArrayList<String>();
	StringBuilder stringBuilder = new StringBuilder();
	public List<String> restoreIpAddresses(String s) {
		restoreIpAddressesHandler(s, 0, 0);
		return result;
	}
	public void restoreIpAddressesHandler(String s, int start, int number) {
		if (start == s.length() && number == 4) {
			result.add(stringBuilder.toString());
			return;
		}
		if (start == s.length() || number == 4) {
			return;
		}
		for (int i = start; i < s.length() && i - start < 3 && Integer.parseInt(s.substring(start, i + 1)) >= 0 && Integer.parseInt(s.substring(start, i + 1)) <= 255; i++) {
			if (i + 1 - start > 1 && s.charAt(start) - '0' == 0) {
				continue;
			}
			stringBuilder.append(s.substring(start, i + 1));
			if (number < 3) {
				stringBuilder.append(".");
			}
			number++;
			restoreIpAddressesHandler(s, i + 1, number);
			number--;
			stringBuilder.delete(start + number, i + number + 2);
		}
	}
}