"One Day together Leetcode" #93. Restore IP Addresses

One Day together Leetcode

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(i) Title

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

For example:
Given "25525511135",

return ["255.255.11.135", "255.255.111.35"]. (Order does not matter)

(ii) Problem solving

Topic: Given a string of characters, determine how many valid IP addresses can be composed

You need to pay attention to invalid IP, such as 00,010, etc in solving process

Problem-solving ideas: The use of backtracking, IP has four levels, respectively, to determine whether each level is effective, in turn recursive, to the final judgment can constitute a valid IP, no back to the previous level to continue recursion. Detailed ideas See code comments

classSolution { Public: vector<string>Restoreipaddresses (strings) { vector<string>Retstringip Dfsrestoreip (S,ip,0,0, ret);returnRet }voidDFSRESTOREIP (string& S,stringIpintCount,intI vector<string>&ret) {if(count==4)//Count to 4 indicates an IP address{if(I==s.length ()) {Ip.erase (Ip.end ()-1);//Remove the last '. 'Ret.push_back (IP); }return; }intnum =0; for(intj = i; J < S.length ();            J + +) {Ip+=s[j]; num = num*Ten+ (s[j]-' 0 ');if(num>0&&s[i]==' 0 ')return;//Remove invalid IPs such as ' 01 ', ' 010 '            if(num==0&&j-i>=1)return;//Remove invalid IPs such as ' 00 '            if(num< the) {ip+='. ';//Plus. Representative to the next levelDfsrestoreip (s,ip,count+1, j+1, ret); Ip.erase (Ip.end ()-1);//Back to the previous level}Else return; }    }};

"One Day together Leetcode" #93. Restore IP Addresses