Group words with same set of characters

Last Updated : 05 Jul, 2025

Given a list of words with lower cases. Implement a function to find all Words that have the same unique character set.

Example:

Input: words[] = { "may", "student", "students", "dog",
"studentssess", "god", "cat", "act",
"tab", "bat", "flow", "wolf", "lambs",
"amy", "yam", "balms", "looped",
"poodle"};
Output :
looped, poodle,
lambs, balms,
flow, wolf,
tab, bat,
may, amy, yam,
student, students, studentssess,
dog, god,
cat, act,
Explanation :
All words with same set of characters are printed together in a line.

The idea is to use hashing. We generate a key for all words. The key contains all unique characters (The size of the key is at most 26 for lowercase alphabets). We store indexes of words as values for a key. Once we have filled all keys and values in the hash table, we can print the result by traversing the table.

Below is the implementation of the above idea.

C++

// C++ program to print all words that have
// the same unique character set
#include<bits/stdc++.h>
using namespace std;
#define MAX_CHAR 26

// Generates a key from given string. The key
// contains all unique characters of given string in
// sorted order consisting of only distinct elements.
string getKey(string &str)
{
    bool visited[MAX_CHAR] = { false };

    // store all unique characters of current
    // word in key
    for (int j = 0; j < str.length(); j++)
        visited[str[j] - 'a'] = true ;
    string key = "";
    for (int j=0; j < MAX_CHAR; j++)
        if (visited[j])
            key = key + (char)('a'+j);
    return key;
}

// Print all words together with same character sets.
void wordsWithSameCharSet(string words[], int n)
{
    // Stores indexes of all words that have same
    // set of unique characters.
    unordered_map <string, vector <int> > Hash;

    // Traverse all words
    for (int i=0; i<n; i++)
    {
        string key = getKey(words[i]);
        Hash[key].push_back(i);
    }

    // print all words that have the same unique character set
    for (auto it = Hash.begin(); it!=Hash.end(); it++)
    {
      for (auto v=(*it).second.begin(); v!=(*it).second.end(); v++)
          cout << words[*v] << ", ";
      cout << endl;
    }
}

// Driver program to test above function
int main()
{
    string words[] = { "may", "student", "students", "dog",
                 "studentssess", "god", "cat", "act", "tab",
                 "bat", "flow", "wolf", "lambs", "amy", "yam",
                 "balms", "looped", "poodle"};
    int n = sizeof(words)/sizeof(words[0]);
    wordsWithSameCharSet(words, n);
    return 0;
}

Java

// Java program to print all words that have
// the same unique character set
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map.Entry;
public class GFG {
 
    static final int MAX_CHAR = 26;
     
    // Generates a key from given string. The key
    // contains all unique characters of given string
    // in sorted order consisting of only distinct elements.
    static String getKey(String str)
    {
        boolean[] visited = new boolean[MAX_CHAR];
        Arrays.fill(visited, false);
     
        // store all unique characters of current
        // word in key
        for (int j = 0; j < str.length(); j++)
            visited[str.charAt(j) - 'a'] = true ;
        String key = "";
        for (int j=0; j < MAX_CHAR; j++)
            if (visited[j])
                key = key + (char)('a'+j);
        return key;
    }
     
    // Print all words together with same character sets.
    static void wordsWithSameCharSet(String words[], int n)
    {
        // Stores indexes of all words that have same
        // set of unique characters.
        //unordered_map <string, vector <int> > Hash;
        HashMap<String, ArrayList<Integer>> Hash = new HashMap<>();
     
        // Traverse all words
        for (int i=0; i<n; i++)
        {
            String key = getKey(words[i]);
            
            // if the key is already in the map
            // then get its corresponding value
            // and update the list and put it in the map
            if(Hash.containsKey(key))
            {
                ArrayList<Integer> get_al = Hash.get(key);
                get_al.add(i);
                Hash.put(key, get_al);
            }
            
            // if key is not present in the map
            // then create a new list and add
            // both key and the list
            else
            {
                ArrayList<Integer> new_al = new ArrayList<>();
                new_al.add(i);
                Hash.put(key, new_al);
            }
        }
     
        // print all words that have the same unique character set
        for (Entry<String, ArrayList<Integer>> it : Hash.entrySet())
        {
            ArrayList<Integer> get =it.getValue();
            for (Integer v:get)
                System.out.print( words[v] + ", ");
            System.out.println();
        }
    }
     
    // Driver program to test above function
    public static void main(String args[])
    {
        String words[] = { "may", "student", "students", "dog",
                     "studentssess", "god", "cat", "act", "tab",
                     "bat", "flow", "wolf", "lambs", "amy", "yam",
                     "balms", "looped", "poodle"};
        int n = words.length;
        wordsWithSameCharSet(words, n);
    }
}
// This code is contributed by Sumit Ghosh

Python

# Python program to print all words that
# have the same unique character set

# Function to group all strings with same characters
from collections import Counter

def groupStrings(input):
    # traverse all strings one by one
    # dict is an empty dictionary
    dict={}
    
    for word in input:
        # sort the current string and take it's
        # sorted value as key
        # sorted return list of sorted characters
        # we need to join them to get key as string
        # Counter() method returns dictionary with frequency of
        # each character as value
        wordDict=Counter(word)

        # now get list of keys
        key = wordDict.keys()

        # now sort these keys
        key = sorted(key)

        # join these characters to produce key string
        key = ''.join(key)
        
        # now check if this key already exist in
        # dictionary or not
        # if exist then simply append current word
        # in mapped list on key
        # otherwise first assign empty list to key and
        # then append current word in it
        if key in dict.keys():
            dict[key].append(word)
        else:
            dict[key]=[]
            dict[key].append(word)

        # now traverse complete dictionary and print
        # list of mapped strings in each key separated by ,
    for (key,value) in dict.items():
        print (','.join(dict[key]))
        
# Driver program
if __name__ == "__main__":
    input=['may','student','students','dog','studentssess','god','cat','act','tab','bat','flow','wolf','lambs','amy','yam','balms','looped','poodle']
    groupStrings(input)

// C# program to print all words that
// have the same unique character set
using System;
using System.Collections.Generic;

class GFG{
 
static readonly int MAX_CHAR = 26;
 
// Generates a key from given string. The
// key contains all unique characters of
// given string in sorted order consisting
// of only distinct elements.
static String getKey(String str)
{
    bool[] visited = new bool[MAX_CHAR];
 
    // Store all unique characters of current
    // word in key
    for(int j = 0; j < str.Length; j++)
        visited[str[j] - 'a'] = true;
        
    String key = "";
    
    for(int j = 0; j < MAX_CHAR; j++)
        if (visited[j])
            key = key + (char)('a' + j);
            
    return key;
}
 
// Print all words together with same character sets.
static void wordsWithSameCharSet(String []words, int n)
{
    
    // Stores indexes of all words that have same
    // set of unique characters.
    //unordered_map <string, vector <int> > Hash;
    Dictionary<String, 
               List<int>> Hash = new Dictionary<String, 
                                                List<int>>();
 
    // Traverse all words
    for (int i = 0; i < n; i++)
    {
        String key = getKey(words[i]);
        
        // If the key is already in the map
        // then get its corresponding value
        // and update the list and put it
        // in the map
        if (Hash.ContainsKey(key))
        {
            List<int> get_al = Hash[key];
            get_al.Add(i);
            Hash[key]= get_al;
        }
        
        // If key is not present in the map
        // then create a new list and add
        // both key and the list
        else
        {
            List<int> new_al = new List<int>();
            new_al.Add(i);
            Hash.Add(key, new_al);
        }
    }
 
    // Print all words that have the 
    // same unique character set
    foreach(KeyValuePair<String, List<int>> it in Hash)
    {
        List<int> get =it.Value;
        foreach(int v in get)
            Console.Write( words[v] + ", ");
            
        Console.WriteLine();
    }
}
 
// Driver code
public static void Main(String []args)
{
    String []words = { "may", "student", "students",
                       "dog", "studentssess", "god",
                       "cat", "act", "tab",
                       "bat", "flow", "wolf", 
                       "lambs", "amy", "yam",
                       "balms", "looped", "poodle"};
                       
    int n = words.Length;
    
    wordsWithSameCharSet(words, n);
}
}

// This code is contributed by Princi Singh

JavaScript

<script>

const MAX_CHAR = 26;

// Generates a key from given string. The key
// contains all unique characters of given string in
// sorted order consisting of only distinct elements.
function getKey(str) {
  let visited = new Array(MAX_CHAR).fill(false);

  // store all unique characters of current
  // word in key
  for (let j = 0; j < str.length; j++) {
    visited[str.charCodeAt(j) - 97] = true;
  }
  let key = "";
  for (let j = 0; j < MAX_CHAR; j++) {
    if (visited[j]) {
      key += String.fromCharCode(97 + j);
    }
  }
  return key;
}

// Print all words together with same character sets.
function wordsWithSameCharSet(words, n) {
  // Stores indexes of all words that have same
  // set of unique characters.
  let Hash = {};

  // Traverse all words
  for (let i = 0; i < n; i++) {
    let key = getKey(words[i]);
    if (key in Hash) {
      Hash[key].push(i);
    } else {
      Hash[key] = [i];
    }
  }

  // print all words that have the same unique character set
  for (let key in Hash) {
    for (let v of Hash[key]) {
      console.log(words[v] + ", ");
    }
    console.log("\n");
  }
}

// Driver program to test above function
function main() {
  let words = [    "may",    "student",    "students",    "dog",    "studentssess",    "god",    "cat",    "act",    "tab",    "bat",    "flow",    "wolf",    "lambs",    "amy",    "yam",    "balms",    "looped",    "poodle",  ];
  let n = words.length;
  wordsWithSameCharSet(words, n);
}

main();


</script>

Output

looped, poodle, 
student, students, studentssess, 
may, amy, yam, 
dog, god, 
cat, act, 
tab, bat, 
lambs, balms, 
flow, wolf,

Time Complexity: O(n*k) where n is number of words in dictionary and k is maximum length of a word.
Auxiliary Space: O(n*k), where n is number of words in dictionary and k is maximum length of a word.

Analysis of Algorithms

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