Given a string containing only digits, restore it by returning all possible valid IP address combinations.git
Example:rest
Input: "25525511135"
Output: ["255.255.11.135", "255.255.111.35"]code
class Solution { public List<String> restoreIpAddresses(String s) { //4 segments, 0-255, dfs from 0 to len-1 List<String> res = new ArrayList<>(); dfs(s, 0, 0, "", res); return res; } private void dfs(String str, int index, int count, String temp, List<String> res) { int n = str.length(); if (count == 4 && index == n) { res.add(temp); return; } if (count > 4 || index > n) return; for (int i = 1; i <= 3; i++) { if (index+i > n) break; String part = str.substring(index, index+i); if (part.startsWith("0") && part.length() != 1 || Integer.parseInt(part) > 255) continue; String cur = temp+part; if (count != 3) cur += "."; dfs(str, index+i, count+1, cur, res); } } }