题目描述

93. Restore IP Addresses

代码

回溯法

class Solution {
    vector<string> res;
public:
    vector<string> restoreIpAddresses(string s) {
        string IP;
        int part = 0;
        backtracking(s,0,IP,part);
        return res;
    }
    void backtracking(const string &s,int start,string &IP,int &part){
        if(start == s.size())
        {
            if(part == 4)
                res.push_back(IP);
            return;
        }

        if(part==4)
            return;

        int iplen = IP.size();
        for(int i = start;i < s.size();i++){
            if(i >start && s[start]=='0')//前导0的数字不考虑
                break;
            int temp = atoi(s.substr(start,i-start+1).c_str());
            if(temp >255)//大于255的不考虑，后面的只会更大，所以break
                break;
            IP += (s.substr(start,i-start+1));
            if(part<3)
                IP.push_back('.');
            part++;
            backtracking(s,i+1,IP,part);
            IP.resize(iplen);
            part--;
        }
    }
};