93.Restore IP Addresses(M)-优快云博客

本文介绍了一种通过递归深度优先搜索(DFS)算法来解决字符串形式的IP地址还原问题的方法。给定一个仅由数字组成的字符串，该算法可以返回所有可能的有效IP地址组合。

Medium

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Given a string containing only digits, restore it by returning all possible valid IP address combinations.

Example:

Input: "25525511135"
Output: ["255.255.11.135", "255.255.111.35"]

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class Solution {
public:
    vector<string> restoreIpAddresses(string s) {
        vector<string> result;
        string ip;
        dfs(s,0,0,ip,result); //paras:string s,start index of s,step(from0-3),intermediate ip,final result
        return result;
    }
    void dfs(string s,int start,int step,string ip,vector<string>& result){
        if(start==s.size()&&step==4){
            ip.erase(ip.end()-1); //remove the last '.' from the last decimal number
            result.push_back(ip);
            return;
        }
        if(s.size()-start>(4-step)*3) return;
        if(s.size()-start<(4-step)) return;
        int num=0;
        for(int i=start;i<start+3;i++){
            num=num*10+(s[i]-'0');
            if(num<=255){
                ip+=s[i];
                dfs(s,i+1,step+1,ip+'.',result);
            }
            if(num==0) break;
        }
    }
};
// zjchenRice