# 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 ` `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 > groupMap = ``new` `HashMap<>();` `        ``for` `(``int` `i = ``0``; i < str.length; i++) {` `            ``String diffStr = getDiffString(str[i]);` `            ``List indices = groupMap.getOrDefault(diffStr, ``new` `ArrayList<>());` `            ``indices.add(i);` `            ``groupMap.put(diffStr, indices);` `        ``}`   `        ``// iterating through map to print group` `        ``for` `(Map.Entry> entry : groupMap.entrySet()) {` `            ``List 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

 ``

Output

```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)

If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Feeling lost in the world of random DSA topics, wasting time without progress? It's time for a change! Join our DSA course, where we'll guide you on an exciting journey to master DSA efficiently and on schedule.
Ready to dive in? Explore our Free Demo Content and join our DSA course, trusted by over 100,000 geeks!

Previous
Next