Restore IP Addresses

Restore IP Addresses

问题：

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

思路：

　　dfs + 回溯模板

我的代码1：

isValid中要catch到 00 0 010是不合法的数据

public class Solution {
public List<String> restoreIpAddresses(String s) {
if(s == null || s.length() < 4 || s.length() > 12)    return list;
helper(s, 0, "");
return list;
}
private List<String> list = new ArrayList<String>();
public void helper(String s, int count, String res)
{
if(count == 4)
{
if(!s.equals("")) return;
list.add(res.substring(1));
return;
}
for(int i = 1; i <= s.length() && i <= 3; i++)
{
String ip = s.substring(0,i);
if(validIp(ip))
{
helper(s.substring(i), count + 1, res + "." + ip);
}
}
}
public boolean validIp(String ip)
{
if(ip.length() > 1 && ip.charAt(0) == '0') return false;
int value = Integer.parseInt(ip);
return value >= 0 && value <= 255;
}
}

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