LeetCode OJ：Restore IP Addresses（存储IP地址）

Given a string containing only digits, restore it by returning all possible valid IP address combinations.

For example:
Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

典型的dfs，但是要点是注意什么才是真的ip地址，代码如下：

class Solution {
public:
    vector<string> restoreIpAddresses(string s) {
        if (s.size() > 12) return ret;
        dfs(s, 0, 0);
        return ret;
    }
    
    bool check(string &s)
    {
        if (s.size() == 1)
            return "0" <= s && s <= "9";
        else if (s.size() == 2)
            return "10" <= s && s <= "99";
        else if (s.size() == 3)
            return "100" <= s && s <= "255";
        else
            return false;
    }

    void dfs(const string & s, int start, int nth)
    {
        if (nth == 4 && start != s.size())
            return;
        else if (nth == 4 && start == s.size()){
            string tmp = "";
            for (int i = 0; i < 3; ++i){
                tmp += tmpRes[i];
                tmp += ".";
            }
            tmp += tmpRes[3];    //为了凑格式
            ret.push_back(tmp);
        }
        else
            for (int i = 1; i < 4; ++i){
                if(start + i <= s.size()){
                    string tmp = s.substr(start, i);
                    if(check(tmp)){
                        tmpRes.push_back(tmp);
                        dfs(s, start + i, nth + 1);
                        tmpRes.pop_back();
                    }
                }
            }
    }

private:
    vector<string> tmpRes;
    vector<string> ret;
};

写的有点乱了 ，见谅见谅