leetcode Restore IP Addresses

最新推荐文章于 2025-09-10 22:21:01 发布

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最新推荐文章于 2025-09-10 22:21:01 发布

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文章标签： java leetcode 回溯

本文链接：https://blog.youkuaiyun.com/u013626088/article/details/41123515

本文详细阐述了如何通过字符串解析生成所有可能的有效IP地址组合，包括处理数字范围、避免无效组合等关键步骤。

Restore IP Addresses 原题地址：

https://oj.leetcode.com/problems/restore-ip-addresses/

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)

每个位置上的数字介于0-255之间，另外注意这个位置上不能出现"01"之类的字符串。

public class Solution {
    private List<String> IP = new ArrayList<String>();
	public List<String> restoreIpAddresses(String s) {
		int max = Math.min(3, s.length() - 3);
		int min = Math.max(1, s.length() - 9);
		
		if (min > 3 || max < 1)
			return IP;
		for (int i = min; i <= max; i++) {
			StringBuffer Temp = new StringBuffer();
			String temp = s.substring(0, i);
			if (temp.charAt(0) == '0' && i > 1)
				break;
			int ip = Integer.parseInt(temp);
			if (ip < 256) {
				Temp.append(s.substring(0, i));
				findIP(Temp, 3, s.substring(i));
			}
		}
		return IP;
	}
	
	private void findIP(StringBuffer Temp, int p, String s) {
		int max = Math.min(3, s.length() - (p-1));
		int min = Math.max(1, s.length() - 3 * (p - 1));
		
		if (min > 3 || max < 1)
			return;
		
		if (p == 1) {
			if (s.charAt(0) == '0' && s.length() > 1)
				return;
			int ip = Integer.parseInt(s);
			if (ip < 256) {
				Temp.append("."+s);
				IP.add(Temp.toString());
			}
			return;
		}
		int start = Temp.length();
	    for (int i = min; i <= max; i++) {
			String temp = s.substring(0, i);
			if (temp.charAt(0) == '0' && temp.length() > 1)
				return;
			int ip = Integer.parseInt(temp);
			if (ip < 256) {
				Temp.append("." + s.substring(0, i));
				findIP(Temp, p-1, s.substring(i));
				Temp.delete(start, Temp.length());
			}
		}
	}
}