leetcode restore ip address Java实现

原题目链接：

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

java代码：

class Solution {
    public List<String> restoreIpAddresses(String s) {
        ArrayList<String> ips=new ArrayList<String>();
        String current_ip="";
        getAllIP(s,0,0,current_ip,ips);
        return ips;
    }
    
    public void getAllIP(String s,int index,int step,String current_ip,ArrayList<String> ips)
    {
        if(s.length()-index>(4-step)*3)
        {
            return;
        }
        else if(s.length()-index<4-step)
        {
            return;
        }
        else if(step==4&&index==s.length())
        {
            ips.add(current_ip.substring(0,current_ip.length()-1));
        }
        else
        {
            int num=0;
            for(int i=index;i<Math.min(index+3,s.length());i++)
            {
                num=num*10+s.charAt(i)-'0';
                if(num<=255)
                {
                    current_ip+=s.charAt(i);
                    getAllIP(s,i+1,step+1,current_ip+".",ips);
                }
                if(num==0) break;
            }
        }
    }
}