Solution.java

public class Solution {
    public List<String> restoreIpAddresses(String s) {
        List<String> answerList=new ArrayList<String>();
        for (int i = 1; i <=3; i++) {
            for (int j = 1; j <=3; j++) {
                for (int k = 1; k <=3; k++) {
                    int[] a={i,j,k};
                    if (i+j+k<s.length()) {
                        String t=new Solution().validate(s, a);
                        if (!(t.equals(""))) {
                            answerList.add(t);
                        }
                    }
                }
            }
        }
        return answerList;
    }
    public String validate(String s,int[] a){
        String s4=s.substring(a[0]+a[1]+a[2],s.length());
        if (s4.length()>3||(s4.length()>1&&s4.substring(0, 1).equals("0"))||Integer.parseInt(s4)>255) {
            return "";
        }
        String s1=s.substring(0,a[0]);
        String s2=s.substring(a[0],a[0]+a[1]);
        String s3=s.substring(a[0]+a[1],a[0]+a[1]+a[2]);
        if ((s3.length()>1&&s3.substring(0, 1).equals("0"))||(s2.length()>1&&s2.substring(0, 1).equals("0"))||(s1.length()>1&&s1.substring(0, 1).equals("0"))||Integer.parseInt(s3)>255||Integer.parseInt(s2)>255||Integer.parseInt(s1)>255) {
            return "";
        }
        return s1+"."+s2+"."+s3+"."+s4;
    }
}