Leetcode题解（2）：L93/Restore IP Addresses

L93: 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)

解题思路：数据量不大，直接三重循环解决，也可以用DFS解决，差不多

class Solution {
public:
    bool isIpNum(string I)
    {
        if(I[0] == ‘0‘ && I.length() != 1)
            return false;
        int num = std::stoi(I);
        if(num >= 0 && num <= 255)
            return true;
        return false;
    }

    vector<string> restoreIpAddresses(string s) {
        vector<string> result;
        int len=s.length();

        if(len<4||len>12)
            return result;  //肯定不满足，直接返回

        string I1,I2,I3,I4;
        //三重循环
        for(int j=1;j<len-2;j++)
        {
            for(int k=j+1;k<len-1;k++)
            {
                for(int t=k+1;t<len;t++)
                {
                    I1 = s.substr(0,j);
                    I2 = s.substr(j,k-j);
                    I3 = s.substr(k,t-k);
                    I4 = s.substr(t,len-k);
                    if(isIpNum(I1)&&isIpNum(I2)&&isIpNum(I3)&&isIpNum(I4))
                    {
                        string IP;
                        IP = I1+"."+I2+"."+I3+"."+I4;
                        result.push_back(IP);
                    }
                }
            }
        }
        return result;       
    }
};