import java.util.ArrayList;
import java.util.List;

class Solution {

    public List<String> res = new ArrayList<>();

    public String[] seg = new String[4];

    public List<String> restoreIpAddresses(String s) {

        dfs(s, 0, 0);
        return res;
    }

    private void dfs(String s, int cnt, int cur) {

        if (cnt == 4) {
            if (cur == s.length()) {
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < 4; i++) {
                    sb.append(seg[i]);
                    if (i < 3) {
                        sb.append('.');
                    }
                }
                res.add(sb.toString());
            }
            return;
        }

        if (cur == s.length()) {
            return;
        }

        if (s.charAt(cur) == '0') {
            seg[cnt] = "0";
            dfs(s, cnt + 1, cur + 1);
        }

        int t = 0;
        for (int start = cur; start < s.length(); start ++) {
            t = t * 10 + (s.charAt(start) - '0');
            if (t > 0 && t <= 255) {
                seg[cnt] = t + "";
                dfs(s, cnt + 1, start + 1);
            } else {
                break;
            }
        }
    }
}