leetcode_c++:Restore IP Addresses(091)

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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)

回溯

class Solution {private:    bool isValid(string s){        if(s.length()>3 || s==""||(s.length()>=2&&s[0]=='0')||(s.length()==3 && s>"255"))            return false;        return true;    }public:    vector<string> restoreIpAddresses(string s) {        int len=s.length();        vector<string> ret;        for(int i=1;i<4 && i<len-2;++i) {            for (int j = 1; j < 4 && i + j < len - 1; ++j)                for (int k = 1; k < 4 && i + j + k < len; ++k) {                    string s1 = s.substr(0, i);                    string s2 = s.substr(i, j);                    string s3 = s.substr(i + j, k);                    string s4 = s.substr(i + j + k);                    if (isValid(s1) && isValid(s2) && isValid(s3) && isValid(s4))                        ret.push_back(s1 + "." + s2 + "." + s3 + "." + s4);                }        }        return ret;    }};

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