leetcode/cpp/0093.cpp at master · xfmeng17/leetcode · GitHub

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class Solution {
public:
  vector<string> restoreIpAddresses(string s) { return func1(s); }

  vector<string> func1(string s) {
    vector<string> res = helper(s, 4);
    return res;
  }

  bool check(string s) {
    if (s.length() < 0 || s.length() > 3) {
      return false;
    }
    if (s.length() == 2 && s[0] == '0') {
      return false;
    }
    if (s.length() == 3 && (s[0] == '0' || stoi(s) > 255)) {
      return false;
    }
    return true;
  }

  vector<string> helper(string str, int cnt) {
    vector<string> res;

    if (str.length() < cnt) {
      return res;
    }

    if (cnt == 1) {
      if (check(str)) {
        res.push_back(str);
        return res;
      }
    }

    if (cnt >= 2) {
      // ** cut 1 as head
      string h1 = str.substr(0, 1);
      if (check(h1)) {
        string r1 = str.substr(1);
        vector<string> sub = helper(r1, cnt - 1);
        if (sub.size() > 0) {
          for (string s : sub) {
            res.push_back(h1 + "." + s);
          }
        }
      }

      // ** cut 2 as head
      string h2 = str.substr(0, 2);
      if (check(h2) && (str.length() >= cnt + 1)) {
        string r2 = str.substr(2);
        vector<string> sub = helper(r2, cnt - 1);
        if (sub.size() > 0) {
          for (string s : sub) {
            res.push_back(h2 + "." + s);
          }
        }
      }

      // ** cut 3 as head
      string h3 = str.substr(0, 3);
      if (check(h3) && (str.length() >= cnt + 2)) {
        string r3 = str.substr(3);
        vector<string> sub = helper(r3, cnt - 1);
        if (sub.size() > 0) {
          for (string s : sub) {
            res.push_back(h3 + "." + s);
          }
        }
      }
    }

    return res;
  }
};