Common characters in n strings

Given n strings, find the common characters in all the strings. In simple words, find characters that appear in all the strings and display them in alphabetical order or lexicographical order.

Note* we’ll be considering that the strings contain lower case letters only.

Examples:

Input :  geeksforgeeks
         gemkstones
         acknowledges
         aguelikes

Output : e g k s

Input :  apple 
         orange

Output : a e

We’ll use two hash arrays of size 26 (for a-z, where 0 is a, and z is 25).
The approach will be simple, if we have seen a character before we’ll mark it and if we haven’t then ignore the character because it is not a common one.

Psuedocode :

commonCharacters :
for i= 0 to n-1:

   // here m is length of ith string 
   for j = 0 to m-1:  
      if ( character seen before ) :
         mark the character
      else : 
         ignore it

display all the marked characters

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

// CPP Program to find all the common characters 
// in n strings 
#include <bits/stdc++.h> 
using namespace std; 
  
const int MAX_CHAR = 26; 
  
void commonCharacters(string str[], int n) 
{ 
    // primary array for common characters  
    // we assume all characters are seen before. 
    bool prim[MAX_CHAR]; 
    memset(prim, true, sizeof(prim)); 
  
    // for each string 
    for (int i = 0; i < n; i++) { 
  
        // secondary array for common characters 
        // Initially marked false 
        bool sec[MAX_CHAR] = { false }; 
  
        // for every character of ith string 
        for (int j = 0; str[i][j]; j++) { 
  
            // if character is present in all  
            // strings before, mark it. 
            if (prim[str[i][j] - 'a']) 
                sec[str[i][j] - 'a'] = true;  
        } 
  
        // copy whole secondary array into primary 
        memcpy(prim, sec, MAX_CHAR); 
    } 
  
    // displaying common characters 
    for (int i = 0; i < 26; i++) 
        if (prim[i]) 
            printf("%c ", i + 'a'); 
} 
  
// Driver's Code 
int main() 
{ 
    string str[] = { "geeksforgeeks", 
                    "gemkstones", 
                    "acknowledges", 
                    "aguelikes" }; 
    int n = sizeof(str)/sizeof(str[0]); 
    commonCharacters(str, n); 
    return 0; 
} 

Java

// Java Program to find all the common characters 
// in n strings 
import java.util.*; 
import java.lang.*; 
  
class GFG { 
  
    static int MAX_CHAR = 26; 
  
    public static void commonCharacters(String str[], 
                                               int n) 
    { 
          
        // primary array for common characters  
        // we assume all characters are seen before. 
        Boolean[] prim = new Boolean[MAX_CHAR]; 
        Arrays.fill(prim, new Boolean(true)); 
  
        // for each string 
        for (int i = 0; i < n; i++) { 
  
            // secondary array for common characters 
            // Initially marked false 
            Boolean[] sec = new Boolean[MAX_CHAR]; 
            Arrays.fill(sec, new Boolean(false)); 
  
            // for every character of ith string 
            for (int j = 0; j < str[i].length(); j++) 
            { 
  
                // if character is present in all  
                // strings before, mark it. 
                if (prim[str[i].charAt(j) - 'a']) 
                sec[str[i].charAt(j) - 'a'] = true;  
            } 
  
            // copy whole secondary array into primary 
            System.arraycopy(sec, 0, prim, 0, MAX_CHAR); 
        } 
  
        // displaying common characters 
        for (int i = 0; i < 26; i++) 
            if (prim[i]){ 
                System.out.print(Character.toChars(i  
                                               + 97)); 
                System.out.print(" "); 
            }  
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        String str[] = { "geeksforgeeks", 
                         "gemkstones", 
                         "acknowledges", 
                         "aguelikes" }; 
                           
        int n = str.length; 
        commonCharacters(str, n); 
    } 
} 
  
// This code is contributed by Prasad Kshirsagar 

Python3

# Python3 Program to find all the  
# common characters in n strings 
MAX_CHAR = 26
  
def commonCharacters(strings, n) : 
      
    # primary array for common characters  
    # we assume all characters are seen before.  
    prim = [True] * MAX_CHAR  
      
    # for each strings  
    for i in range(n): 
          
        # secondary array for common characters  
        # Initially marked false  
        sec = [False] * MAX_CHAR  
  
        # for every character of ith strings  
        for j in range(len(strings[i])): 
  
            # if character is present in all  
            # strings before, mark it.  
            if (prim[ord(strings[i][j]) - ord('a')]) : 
                sec[ord(strings[i][j]) - 
                    ord('a')] = True
  
        # copy whole secondary array 
        # into primary  
        for i in range(MAX_CHAR): 
            prim[i] = sec[i] 
  
    # displaying common characters  
    for i in range(26): 
        if (prim[i]) : 
            print("%c " % (i + ord('a')),  
                               end = "") 
  
# Driver's Code  
strings = [ "geeksforgeeks", "gemkstones",  
            "acknowledges", "aguelikes" ] 
n = len(strings) 
commonCharacters(strings, n)  
  
# This code is contributed by Niwesh Gupta 

C#

// C# Program to find all the  
// common characters in n strings 
using System;  
  
class GFG  
{ 
  
    static int MAX_CHAR = 26; 
  
    public static void commonCharacters(String []str, 
                                            int n) 
    { 
          
        // primary array for common characters  
        // we assume all characters are seen before. 
        Boolean[] prim = new Boolean[MAX_CHAR]; 
          
        for(int i = 0; i < prim.Length; i++) 
            prim[i] = true; 
  
        // for each string 
        for (int i = 0; i < n; i++) 
        { 
  
            // secondary array for common characters 
            // Initially marked false 
            Boolean[] sec = new Boolean[MAX_CHAR]; 
              
            for(int s = 0; s < sec.Length; s++) 
                sec[s]=false; 
  
            // for every character of ith string 
            for (int j = 0; j < str[i].Length; j++) 
            { 
  
                // if character is present in all  
                // strings before, mark it. 
                if (prim[str[i][j] - 'a']) 
                sec[str[i][j] - 'a'] = true;  
            } 
  
            // Copy whole secondary array into primary 
            Array.Copy(sec, 0, prim, 0, MAX_CHAR); 
        } 
  
        // Displaying common characters 
        for (int i = 0; i < 26; i++) 
            if (prim[i]) 
            { 
                Console.Write((char)(i + 97)); 
                Console.Write(" "); 
            }  
    } 
  
    // Driver code 
    public static void Main(String[] args) 
    { 
        String []str = { "geeksforgeeks", 
                        "gemkstones", 
                        "acknowledges", 
                        "aguelikes" }; 
                          
        int n = str.Length; 
        commonCharacters(str, n); 
    } 
} 
  
// This code is contributed by Rajput-JI 

Output:

e g k s

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My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

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