Group Shifted String
Given an array of strings (all lowercase letters), the task is to group them in such a way that all strings in a group are shifted versions of each other. Two string S and T are called shifted if,
S.length = T.length and S[i] = T[i] + K for 1 <= i <= S.length for a constant integer K
For example strings, {acd, dfg, wyz, yab, mop} are shifted versions of each other.
Input : str[] = {"acd", "dfg", "wyz", "yab", "mop", "bdfh", "a", "x", "moqs"}; Output : a x acd dfg wyz yab mop bdfh moqs All shifted strings are grouped together.
We can see a pattern among the string of one group, the difference between consecutive characters for all character of the string are equal. As in the above example take acd, dfg and mop
a c d -> 2 1
d f g -> 2 1
m o p -> 2 1
Since the differences are the same, we can use this to identify strings that belong to the same group. The idea is to form a string of differences as key. If a string with the same difference string is found, then this string also belongs to the same group. For example, the above three strings have the same difference string, which is “21”.
In the below implementation, we add ‘a’ to every difference and store 21 as “ba”.
C++
/* C/C++ program to print groups of shifted strings together. */ #include <bits/stdc++.h> using namespace std; const int ALPHA = 26; // Total lowercase letter // Method to a difference string for a given string. // If string is "adf" then difference string will be // "cb" (first difference 3 then difference 2) string getDiffString(string str) { string shift = "" ; for ( int i = 1; i < str.length(); i++) { int dif = str[i] - str[i-1]; if (dif < 0) dif += ALPHA; // Representing the difference as char shift += (dif + 'a' ); } // This string will be 1 less length than str return shift; } // Method for grouping shifted string void groupShiftedString(string str[], int n) { // map for storing indices of string which are // in same group map< string, vector< int > > groupMap; for ( int i = 0; i < n; i++) { string diffStr = getDiffString(str[i]); groupMap[diffStr].push_back(i); } // iterating through map to print group for ( auto it=groupMap.begin(); it!=groupMap.end(); it++) { vector< int > v = it->second; for ( int i = 0; i < v.size(); i++) cout << str[v[i]] << " " ; cout << endl; } } // Driver method to test above methods int main() { string str[] = { "acd" , "dfg" , "wyz" , "yab" , "mop" , "bdfh" , "a" , "x" , "moqs" }; int n = sizeof (str)/ sizeof (str[0]); groupShiftedString(str, n); return 0; } |
Java
//Java code for above approach import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class ShiftedStrings { public static final int ALPHA = 26 ; // Method to a difference string for a given string. // If string is "adf" then difference string will be // "cb" (first difference 3 then difference 2) public static String getDiffString(String str) { String shift = "" ; for ( int i = 1 ; i < str.length(); i++) { int dif = str.charAt(i) - str.charAt(i - 1 ); if (dif < 0 ) dif += ALPHA; // Representing the difference as char shift += ( char )(dif + 'a' ); } // This string will be 1 less length than str return shift; } // Method for grouping shifted string public static void groupShiftedString(String[] str) { // map for storing indices of string which are // in same group Map< String, List<Integer> > groupMap = new HashMap<>(); for ( int i = 0 ; i < str.length; i++) { String diffStr = getDiffString(str[i]); List<Integer> indices = groupMap.getOrDefault(diffStr, new ArrayList<>()); indices.add(i); groupMap.put(diffStr, indices); } // iterating through map to print group for (Map.Entry<String, List<Integer>> entry : groupMap.entrySet()) { List<Integer> v = entry.getValue(); for ( int i = 0 ; i < v.size(); i++) System.out.print(str[v.get(i)] + " " ); System.out.println(); } } // Driver method to test above methods public static void main(String[] args) { String[] str = { "acd" , "dfg" , "wyz" , "yab" , "mop" , "bdfh" , "a" , "x" , "moqs" }; groupShiftedString(str); } } // This code is contributed by adityamaharshi21 |
Python3
# Python3 program to print groups # of shifted strings together. # Total lowercase letter ALPHA = 26 # Method to a difference string # for a given string. If string # is "adf" then difference string # will be "cb" (first difference # 3 then difference 2) def getDiffString( str ): shift = "" for i in range ( 1 , len ( str )): dif = ( ord ( str [i]) - ord ( str [i - 1 ])) if (dif < 0 ): dif + = ALPHA # Representing the difference # as char shift + = chr (dif + ord ( 'a' )) # This string will be 1 less # length than str return shift # Method for grouping # shifted string def groupShiftedString( str ,n): # map for storing indices # of string which are # in same group groupMap = {} for i in range (n): diffStr = getDiffString( str [i]) if diffStr not in groupMap: groupMap[diffStr] = [i] else : groupMap[diffStr].append(i) # Iterating through map # to print group for it in groupMap: v = groupMap[it] for i in range ( len (v)): print ( str [v[i]], end = " " ) print () # Driver code str = [ "acd" , "dfg" , "wyz" , "yab" , "mop" , "bdfh" , "a" , "x" , "moqs" ] n = len ( str ) groupShiftedString( str , n) # This code is contributed by avanitrachhadiya2155 |
C#
using System; using System.Collections.Generic; public class ShiftedStrings { public static readonly int ALPHA = 26; // Method to a difference string for a given string. // If string is "adf" then difference string will be // "cb" (first difference 3 then difference 2) public static string GetDiffString( string str) { string shift = "" ; for ( int i = 1; i < str.Length; i++) { int dif = str[i] - str[i - 1]; if (dif < 0) dif += ALPHA; // Representing the difference as char shift += ( char )(dif + 'a' ); } // This string will be 1 less length than str return shift; } // Method for grouping shifted string public static void GroupShiftedString( string [] str) { // map for storing indices of string which are // in same group Dictionary< string , List< int > > groupMap = new Dictionary< string , List< int > >(); for ( int i = 0; i < str.Length; i++) { string diffStr = GetDiffString(str[i]); List< int > indices; if (!groupMap.ContainsKey(diffStr)) { indices = new List< int >(); } else { indices = groupMap[diffStr]; } indices.Add(i); groupMap[diffStr] = indices; } // iterating through map to print group foreach (KeyValuePair< string , List< int > > entry in groupMap) { List< int > v = entry.Value; for ( int i = 0; i < v.Count; i++) Console.Write(str[v[i]] + " " ); Console.WriteLine(); } } // Driver method to test above methods public static void Main( string [] args) { string [] str = { "acd" , "dfg" , "wyz" , "yab" , "mop" , "bdfh" , "a" , "x" , "moqs" }; GroupShiftedString(str); } } // This code is contributed by aadityamaharshi21. |
Javascript
<script> /* Javascript program to print groups of shifted strings together. */ let ALPHA = 26; // Method to a difference string for a given string. // If string is "adf" then difference string will be // "cb" (first difference 3 then difference 2) function getDiffString(str) { let shift = "" ; for (let i = 1; i < str.length; i++) { let dif = str[i] - str[i-1]; if (dif < 0) dif += ALPHA; // Representing the difference as char shift += (dif + 'a' ); } // This string will be 1 less length than str return shift; } // Method for grouping shifted string function groupShiftedString(str, n) { // map for storing indices of string which are // in same group let groupMap = new Map(); for (let i = 0; i < n; i++) { let diffStr = getDiffString(str[i]); if (!groupMap.has(diffStr)) groupMap.set(diffStr,[]); groupMap.get(diffStr).push(i); } // iterating through map to print group for (let [key, value] of groupMap.entries()) { let v = value; for (let i = 0; i < v.length; i++) document.write(str[v[i]]+ " " ); document.write( "<br>" ) } } // Driver method to test above methods let str=[ "acd" , "dfg" , "wyz" , "yab" , "mop" , "bdfh" , "a" , "x" , "moqs" ]; let n = str.length; groupShiftedString(str, n); // This code is contributed by ab2127 </script> |
a x acd dfg wyz yab mop bdfh moqs
Time Complexity: O(N*K), where N=length of string array and K is maximum length of string in string array
Auxiliary Space: O(N)