Leetcode 93.复制IP地址

复制IP地址

给定一个只包含数字的字符串，复原它并返回所有可能的 IP 地址格式。

示例:

输入: "25525511135"

输出: ["255.255.11.135", "255.255.111.35"]

 import java.util.ArrayList;
 import java.util.List;

 class Solution {
     private List<String> result  = new ArrayList<>();
     int length;
     public List<String> restoreIpAddresses(String s) {
         length = s.length();
         int[] ip = new int[4];
         restoreIpAddresses(s,0,ip,0);
         return result;
     }
     private void restoreIpAddresses(String s, int si, int[] ip, int pi) {
         int sl = length - si , pl = 3 - pi , i = -1;
         String pfx = null;
         while (si< length){
             int num = s.charAt(si++) - '1' + 1;
             if (i==0) break;
             i = i == -1 ? num : i * 10 + num;
             sl--;
             if (i>255) break;
             if (sl < pl || sl > pl * 3) continue;
             if (pi==3){
                 if (pfx==null){
                     StringBuilder pfxBuilder = new StringBuilder();
                     for (int j = 0; j < ip.length-1; j++) pfxBuilder.append(ip[j]).append('.');
                     pfx = pfxBuilder.toString();
                 }
                 result.add(pfx + i);
             }
             ip[pi] = i;
             restoreIpAddresses(s,si,ip,pi+1);
         }
     }
 }