import java.util.ArrayList;public class Solution {ArrayList<String> rt = new ArrayList<String>();ArrayList<Integer> cand = new ArrayList<Integer>();String str;public ArrayList<String> restoreIpAddresses(String s) {// Start typing your Java solution below// DO NOT write main() function
        rt.clear();cand.clear();str = s;if (s.length() > 12)return rt;dfs(0);return rt;}//index 是当前检测的第一个字符private void dfs(int index) {//终止条件，已经检测到合法的candidate，那么添加到结果集if (cand.size() == 4 && index == str.length()) {addCandToRt();}//因为1位和2位数字肯定小于255，所以直接往更深搜索if (index >= str.length() || cand.size() >= 4)return;cand.add(Integer.parseInt(str.substring(index, index+1)));dfs(index+1);cand.remove(cand.size()-1);if (index >= str.length()-1 || str.substring(index, index+1).equals("0") || cand.size() >= 4)return;cand.add(Integer.parseInt(str.substring(index, index+2)));dfs(index+2);cand.remove(cand.size()-1);if (index >= str.length()-2 || str.substring(index, index+1).equals("0") || cand.size() >= 4)return;if (Integer.parseInt(str.substring(index, index+3)) <= 255) {cand.add(Integer.parseInt(str.substring(index, index+3)));dfs(index+3);cand.remove(cand.size()-1);}}private void addCandToRt() {String ip = cand.get(0) + "."+ cand.get(1) + "."+ cand.get(2) + "."+ cand.get(3);rt.add(ip);}public static void main(String[] args) {String s = "010010";Solution sl = new Solution();ArrayList<String> all = sl.restoreIpAddresses(s);for (int i = 0; i < all.size(); i++) {System.out.println(all.get(i));}}
}