複製IP地址

給定一個只包含數字的字串，復原它並返回所有可能的 IP 地址格式。

示例:

輸入: "25525511135"

輸出: ["255.255.11.135", "255.255.111.35"]

 1 import java.util.ArrayList;
 2 import java.util.List;
 3 
 4 class Solution {
 5     private List<String> result  = new ArrayList<>();
 6     int length;
 7     public
 
 List<String> restoreIpAddresses(String s) {
 8         length = s.length();
 9         int[] ip = new int[4];
10         restoreIpAddresses(s,0,ip,0);
11         return result;
12     }
13     private void restoreIpAddresses(String s, int si, int[] ip, int pi) {
14         int sl = length - si , pl = 3 - pi , i = -1;
 
15         String pfx = null;
16         while (si< length){
17             int num = s.charAt(si++) - '1' + 1;
18             if (i==0) break;
19             i = i == -1 ? num : i * 10 + num;
20             sl--;
21             if (i>255) break;
22             if (sl < pl || sl > pl * 3) continue
 
;
23             if (pi==3){
24                 if (pfx==null){
25                     StringBuilder pfxBuilder = new StringBuilder();
26                     for (int j = 0; j < ip.length-1; j++) pfxBuilder.append(ip[j]).append('.');
27                     pfx = pfxBuilder.toString();
28                 }
29                 result.add(pfx + i);
30             }
31             ip[pi] = i;
32             restoreIpAddresses(s,si,ip,pi+1);
33         }
34     }
35 }
36