一、题目内容

二、题解

解法1：

思路

全排列+剪枝

代码

public class Solution {
    private ArrayList<String> res = new ArrayList<String>();
    public ArrayList<String> restoreIpAddresses (String s) {
        ArrayList<String> parts = new ArrayList<String>();
        recur(s,0,parts);
        return res;
    }
    private void recur(String str,int startIdx,ArrayList<String> parts){
        if(parts.size() == 4){
            String a = parts.get(0);
            String b = parts.get(1);
            String c = parts.get(2);
            String d = parts.get(3);
            if(a.length() + b.length() + c.length() + d.length() == str.length()) {
                res.add(a + "." + b + "." + c + "." + d);
            }
            return;
        }
        for(int i = startIdx; i<str.length()&&i<startIdx+3;i++){
            String subStr = str.substring(startIdx,i+1);
            Integer subNum = Integer.parseInt(subStr);
            if(subNum>=0&&subNum<=255){
                parts.add(subNum.toString());
                recur(str,i+1,parts);
                parts.remove(parts.size()-1);
            }
        }
    }
}