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)
public class Solution { public List<String> restoreIpAddresses(String s) { List<String> solutions = new ArrayList<String>(); restoreIp(s, solutions, 0, "", 0); return solutions; } private void restoreIp(String ip, List<String> solutions, int idx, String restored, int count) { if (count > 4) return; if (count == 4 && idx == ip.length()) solutions.add(restored); for (int i=1; i<4; i++) { if (idx+i > ip.length()) break; String s = ip.substring(idx,idx+i); if ((s.startsWith("0") && s.length()>1) || (i==3 && Integer.parseInt(s) >= 256)) continue; restoreIp(ip, solutions, idx+i, restored+s+(count==3?"" : "."), count+1); } } }
原文:http://www.cnblogs.com/code-swan/p/4141188.html