249. Group Shifted Strings

Given a string, we can "shift" each of its letter to its successive letter, for example: "abc" -> "bcd". We can keep "shifting" which forms the sequence:

"abc" -> "bcd" -> ... -> "xyz"

Given a list of strings which contains only lowercase alphabets, group all strings that belong to the same shifting sequence.

For example, given: ["abc", "bcd", "acef", "xyz", "az", "ba", "a", "z"], 
A solution is:

[
  ["abc","bcd","xyz"],
  ["az","ba"],
  ["acef"],
  ["a","z"]
]

 

class Solution {
public:
    vector<vector<string>> groupStrings(vector<string>& strings) {
         unordered_map<string,vector<string>>mp;
         for(auto str:strings){
             string t = shifted(str);
             mp[t].push_back(str);
         }
         for(auto it = mp.begin();it!=mp.end();it++)
             sort(it->second.begin(),it->second.end());
         vector<vector<string>> res;
         for(auto it = mp.begin();it!=mp.end();it++)
             res.push_back(it->second);
        return res;
    }
private:
     string shifted(string str)
     {
         string t;
         int diff=0;
         for(int i = 1;i<str.size();i++)
         {
             diff = str[i]-str[i-1];
             if(diff<0) diff+=26;
             t+=to_string(diff)+"#";
         }
         return t;
     }
};