Leetcode题解（2）：L93/Restore IP Addresses

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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;           }};

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