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Find uncommon characters of the two strings

  • Difficulty Level : Easy
  • Last Updated : 08 Jun, 2021

Find and print the uncommon characters of the two given strings in sorted order. Here uncommon character means that either the character is present in one string or it is present in other string but not in both. The strings contain only lowercase characters and can contain duplicates. 
Source: Amazon Interview Experience | Set 355 (For 1 Year Experienced)
Examples: 
 

Input: str1 = “characters”, str2 = “alphabets” 
Output: b c l p r
Input: str1 = “geeksforgeeks”, str2 = “geeksquiz” 
Output: f i o q r u z

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Naive Approach: Using two loops, for each character of 1st string check whether it is present in the 2nd string or not. Likewise, for each character of 2nd string check whether it is present in the 1st string or not.
Time Complexity: O(n^2) and extra would be required to handle duplicates.
Efficient Approach: An efficient approach is to use hashing. 
 



  • Use a hash table of size 26 for all the lowercase characters.
  • Initially, mark presence of each character as ‘0’ (denoting that the character is not present in both the strings).
  • Traverse the 1st string and mark presence of each character of 1st string as ‘1’ (denoting 1st string) in the hash table.
  • Now, traverse the 2nd string. For each character of 2nd string, check whether its presence in the hash table is ‘1’ or not. If it is ‘1’, then mark its presence as ‘-1’ (denoting that the character is common to both the strings), else mark its presence as ‘2’ (denoting 2nd string).

Below image is a dry run of the above approach:
 

Below is the implementation of the above approach:
 

C++




// C++ implementation to find the uncommon
// characters of the two strings
#include <bits/stdc++.h>
using namespace std;
 
// size of the hash table
const int MAX_CHAR = 26;
 
// function to find the uncommon characters
// of the two strings
void findAndPrintUncommonChars(string str1, string str2)
{
    // mark presence of each character as 0
    // in the hash table 'present[]'
    int present[MAX_CHAR];
    for (int i=0; i<MAX_CHAR; i++)
        present[i] = 0;
 
    int l1 = str1.size();
    int l2 = str2.size();
 
    // for each character of str1, mark its
    // presence as 1 in 'present[]'
    for (int i=0; i<l1; i++)
        present[str1[i] - 'a'] = 1;
 
    // for each character of str2
    for (int i=0; i<l2; i++)
    {
        // if a character of str2 is also present
        // in str1, then mark its presence as -1
        if (present[str2[i] - 'a'] == 1
            || present[str2[i] - 'a'] == -1)
            present[str2[i] - 'a'] = -1;
 
        // else mark its presence as 2
        else
            present[str2[i] - 'a'] = 2;
    }
 
    // print all the uncommon characters
    for (int i=0; i<MAX_CHAR; i++)
        if (present[i] == 1 || present[i] == 2 )
            cout << (char(i + 'a')) << " ";
}
 
// Driver program to test above
int main()
{
    string str1 = "characters";
    string str2 = "alphabets";
    findAndPrintUncommonChars(str1, str2);
    return 0;
}
Java



// Java implementation to find the uncommon
// characters of the two strings
class GFG
{
 
    // size of the hash table
    static int MAX_CHAR = 26;
 
    // function to find the uncommon
    // characters of the two strings
    static void findAndPrintUncommonChars(String str1,
                                       String str2)
    {
        // mark presence of each character as 0
        // in the hash table 'present[]'
        int present[] = new int[MAX_CHAR];
        for (int i = 0; i < MAX_CHAR; i++)
        {
            present[i] = 0;
        }
 
        int l1 = str1.length();
        int l2 = str2.length();
 
        // for each character of str1, mark its
        // presence as 1 in 'present[]'
        for (int i = 0; i < l1; i++)
        {
            present[str1.charAt(i) - 'a'] = 1;
        }
 
        // for each character of str2
        for (int i = 0; i < l2; i++)
        {
             
            // if a character of str2 is also present
            // in str1, then mark its presence as -1
            if (present[str2.charAt(i) - 'a'] == 1
                || present[str2.charAt(i) - 'a'] == -1)
            {
                present[str2.charAt(i) - 'a'] = -1;
            }
             
            // else mark its presence as 2
            else
            {
                present[str2.charAt(i) - 'a'] = 2;
            }
        }
 
        // print all the uncommon characters
        for (int i = 0; i < MAX_CHAR; i++)
        {
            if (present[i] == 1 || present[i] == 2)
            {
                System.out.print((char) (i + 'a') + " ");
            }
        }
    }
 
    // Driver code
    public static void main(String[] args)
    {
        String str1 = "characters";
        String str2 = "alphabets";
        findAndPrintUncommonChars(str1, str2);
    }
}
 
// This code is contributed by Rajput-JI
Python 3



# Python 3 implementation to find the
# uncommon characters of the two strings
 
# size of the hash table
MAX_CHAR = 26
 
# function to find the uncommon characters
# of the two strings
def findAndPrintUncommonChars(str1, str2):
     
    # mark presence of each character as 0
    # in the hash table 'present[]'
    present = [0] * MAX_CHAR
    for i in range(0, MAX_CHAR):
        present[i] = 0
 
    l1 = len(str1)
    l2 = len(str2)
     
    # for each character of str1, mark its
    # presence as 1 in 'present[]'
    for i in range(0, l1):
        present[ord(str1[i]) - ord('a')] = 1
         
    # for each character of str2
    for i in range(0, l2):
         
        # if a character of str2 is also present
        # in str1, then mark its presence as -1
        if(present[ord(str2[i]) - ord('a')] == 1 or
           present[ord(str2[i]) - ord('a')] == -1):
            present[ord(str2[i]) - ord('a')] = -1
 
        # else mark its presence as 2
        else:
            present[ord(str2[i]) - ord('a')] = 2
 
    # print all the uncommon characters
    for i in range(0, MAX_CHAR):
        if(present[i] == 1 or present[i] == 2):
            print(chr(i + ord('a')), end = " ")
 
# Driver Code
if __name__ == "__main__":
    str1 = "characters"
    str2 = "alphabets"
    findAndPrintUncommonChars(str1, str2)
 
# This code is contributed
# by Sairahul099
C#



// C# implementation to find the uncommon
// characters of the two strings
using System;
 
class GFG
{
 
    // size of the hash table
    static int MAX_CHAR = 26;
 
    // function to find the uncommon
    // characters of the two strings
    static void findAndPrintUncommonChars(String str1,
                                    String str2)
    {
        // mark presence of each character as 0
        // in the hash table 'present[]'
        int []present = new int[MAX_CHAR];
        for (int i = 0; i < MAX_CHAR; i++)
        {
            present[i] = 0;
        }
 
        int l1 = str1.Length;
        int l2 = str2.Length;
 
        // for each character of str1, mark its
        // presence as 1 in 'present[]'
        for (int i = 0; i < l1; i++)
        {
            present[str1[i] - 'a'] = 1;
        }
 
        // for each character of str2
        for (int i = 0; i < l2; i++)
        {
             
            // if a character of str2 is also present
            // in str1, then mark its presence as -1
            if (present[str2[i] - 'a'] == 1
                || present[str2[i] - 'a'] == -1)
            {
                present[str2[i] - 'a'] = -1;
            }
             
            // else mark its presence as 2
            else
            {
                present[str2[i] - 'a'] = 2;
            }
        }
 
        // print all the uncommon characters
        for (int i = 0; i < MAX_CHAR; i++)
        {
            if (present[i] == 1 || present[i] == 2)
            {
                Console.Write((char) (i + 'a') + " ");
            }
        }
    }
 
    // Driver code
    public static void Main(String[] args)
    {
        String str1 = "characters";
        String str2 = "alphabets";
        findAndPrintUncommonChars(str1, str2);
    }
}
 
// This code is contributed by PrinciRaj1992
Javascript



<script>
// Javascript implementation to find the uncommon
// characters of the two strings
 
// size of the hash table
var MAX_CHAR = 26;
 
// function to find the uncommon characters
// of the two strings
function findAndPrintUncommonChars(str1, str2)
{
    // mark presence of each character as 0
    // in the hash table 'present[]'
    var present = Array(MAX_CHAR);
    for (var i = 0; i < MAX_CHAR; i++)
        present[i] = 0;
 
    var l1 = str1.length;
    var l2 = str2.length;
 
    // for each character of str1, mark its
    // presence as 1 in 'present[]'
    for (var i = 0; i < l1; i++)
        present[str1[i].charCodeAt(0) - 'a'.charCodeAt(0)] = 1;
 
    // for each character of str2
    for (var i = 0; i < l2; i++)
    {
        // if a character of str2 is also present
        // in str1, then mark its presence as -1
        if (present[str2[i].charCodeAt(0) - 'a'.charCodeAt(0)] == 1
            || present[str2[i].charCodeAt(0) - 'a'.charCodeAt(0)] == -1)
            present[str2[i].charCodeAt(0) - 'a'.charCodeAt(0)] = -1;
 
        // else mark its presence as 2
        else
            present[str2[i].charCodeAt(0) - 'a'.charCodeAt(0)] = 2;
    }
 
    // print all the uncommon characters
    for (var i=0; i<MAX_CHAR; i++)
        if (present[i] == 1 || present[i] == 2 )
            document.write( (String.fromCharCode(i + 'a'.charCodeAt(0))) + " ");
}
 
// Driver program to test above
var str1 = "characters";
var str2 = "alphabets";
findAndPrintUncommonChars(str1, str2);
 
// This code is contributed by importantly.
</script>
Output: 
 
b c l p r
Time Complexity: O(m + n), where m and n are the sizes of the two strings respectively.
This article is contributed by Ayush Jauhari. 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.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 



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