LeetCode 93.Restore IP Addresses (复原IP地址)

题目描述：

给定一个只包含数字的字符串，复原它并返回所有可能的 IP 地址格式。

示例:

输入: "25525511135"
输出: ["255.255.11.135", "255.255.111.35"]

 

AC C++ Solution:

class Solution {
public:
    vector restoreIpAddresses(string s) {
        vector 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) {
                    ans = to_string(A) + "." + to_string(B) + "." + to_string(C) + "." + to_string(D);
                    if(ans.length() == s.length() + 3)
                        ret.push_back(ans);
                }
            }
        return ret;
    }
};