Leetcode OJ : Restore IP Addresses backtrack暴搜 C++ solution

 1 class Solution {

 2     public:

 3     vector<string> ret;

 4     string src;

 5     int len;

 6     unordered_set<string> added;

 7     vector<string> restoreIpAddresses(string s) {

 8         if ( s.empty() )  return ret;

 9         src = s;

10         len = src.size();

11         backTrack(0,0,  "");

12         return ret;

13     }

14 

15     void backTrack(int pos, int dot_cnt, string substr) {

16         if ( dot_cnt > 4 ) return;

17         if ( pos >= len && dot_cnt == 4 ) {

18             substr.pop_back();

19             if ( added.find(substr) == added.end() ) {

20                 ret.push_back( substr );

21                 added.insert( substr );

22             }

23             return;

24         }

25         char buffer[16];

26         int tx = len - pos > 3 ? 3 : len - pos;

27         for ( int i = 1; i <= tx; i++ ) {

28             string temp = src.substr( pos, i );

29             int number = atoi( temp.c_str() );

30             sprintf( buffer, "%d", number );

31             string str(buffer);

32             if ( str != temp ) continue;

33             string newsub = substr + temp + ".";

34             if ( number >= 0 && number <= 255 ) {

35                 backTrack( pos + i, dot_cnt + 1,  newsub );

36             }

37         }

38     }

39 };