LeetCode:Restore IP Addresses

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)

用C++写的，暴力搜索，加上限制条件，以后考虑是否有改进的地方，这个题目的搜索空间较小、限制条件多，运行速度也很快

class Solution {

public:

    vector<string> restoreIpAddresses(string s) {

        int length = 0;

        vector<string> vs;

        length = s.size();

        int a = 1 , b = 1 , c = 1 , d = 1;

        int tok = 0;

        int tmp = 0;

        for(a=1;a<4;a++){

            if(s[0]=='0' && a>1) break;

            for(b=1;b<4;b++){

                if(s[a]=='0' && b>1) break;

                if(a==3){

                    if(s[0]!='2' && s[0]!='1'){

                        break;

                    }

                    tmp = (s[1]-'0');

                    if(tmp > 5 && s[0] == '2') break;

                }

                for(c=1;c<4;c++){

                    if(s[a+b]=='0' && c>1) break;

                    if(b==3){

                        if(s[a]!='2'&&s[a]!='1') break;

                        tmp = (s[a+1]-'0');

                        if(tmp > 5 && s[a] == '2') break;

                    }

                    for(d=1;d<4;d++){

                        if(s[a+b+c]=='0' && d>1) break;

                        if(c==3){

                            if(s[a+b]!='2'&&s[a+b]!='1') break;

                            tmp = (s[a+b+1] - '0');

                            if(tmp > 5 && s[a+b] == '2') break;

                        }

                        if((a+b+c+d)==length){

                            tok = stoi(s.substr(a+b+c,d));

                            if(tok>255) break;

                            string rt = s.substr(0,a) + "." + s.substr(a,b) + "." + s.substr(a+b,c) + "." + s.substr(a+b+c,d);

                            vs.push_back(rt);

                        }

                    }

                }

            }

        }

        return vs;

    }

};

 改进思路1：内层循环的次数可以改成由上一层限制，想了一下不太对，还要调用min，最后差距不大