leetcode_c++:Restore IP Addresses(091)

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)

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回溯

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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 && i2;++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;

    }
};