GroupShiftedStrings.java

package easy;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class GroupShiftedStrings {

    public List<List<String>> groupStrings(String[] strings) {
     
        List<List<String>> result = new ArrayList<List<String>>();
        Map<String, List<String>> map = new HashMap<String, List<String>>();
        
        for(String word : strings){
            String key = "";
            int offset = word.charAt(0) - 'a';
            for(int i = 1; i < word.length(); i++){
                key += (word.charAt(i) - offset + 26)%26;
            }
            
            if(!map.containsKey(key)) map.put(key, new ArrayList<String>());
            map.get(key).add(word);
        }
        
        for(List<String> list : map.values()){
            Collections.sort(list);  
            result.add(list);            
        } 
        
        return result;
       
    }

}