93. Restore IP Addresses

无敌代码暴力。。。。。，2刷还是乖乖dfs吧

class Solution {public:    vector<string> restoreIpAddresses(string s) {        vector<string> ret;        string ans;        for (int a=1; a<=3; a++)        for (int b=1; b<=3; b++)        for (int c=1; c<=3; c++)        for (int d=1; d<=3; d++)            if (a+b+c+d == s.length()) {                int A = stoi(s.substr(0, a));                int B = stoi(s.substr(a, b));                int C = stoi(s.substr(a+b, c));                int D = stoi(s.substr(a+b+c, d));                if (A<=255 && B<=255 && C<=255 && D<=255)                    if ( (ans=to_string(A)+"."+to_string(B)+"."+to_string(C)+"."+to_string(D)).length() == s.length()+3)                        ret.push_back(ans);            }            return ret;    }};