Remove characters from the first string which are present in the second string

Write an efficient C function that takes two strings as arguments and removes the characters from first string which are present in second string (mask string).

We strongly recommend that you click here and practice it, before moving on to the solution.


Algorithm: Let first input string be”test string” and the string which has characters to be removed from first string be “mask”
1: Initialize:
res_ind = 0 /* index to keep track of processing of each character in i/p string */
ip_ind = 0 /* index to keep track of processing of each character in the resultant string */

2: Construct count array from mask_str. Count array would be:
(We can use Boolean array here instead of int count array because we don’t need count, we need to know only if character is present in mask string)
count[‘a’] = 1
count[‘k’] = 1
count[‘m’] = 1
count[‘s’] = 1

3: Process each character of the input string and if count of that character is 0 then only add the character to the resultant string.
str = “tet tringng” // ’s’ has been removed because ’s’ was present in mask_str but we we have got two extra characters “ng”
ip_ind = 11
res_ind = 9

4: Put a ‘\0′ at the end of the string?



Implementations:

C

filter_none

edit
close

play_arrow

link
brightness_4
code

#include <stdio.h>
#include <stdlib.h>
#define NO_OF_CHARS 256
  
/* Returns an array of size 256 containg count
   of characters in the passed char array */
int *getCharCountArray(char *str)
{
   int *count = (int *)calloc(sizeof(int), NO_OF_CHARS);
   int i;
   for (i = 0; *(str+i);  i++)
      count[*(str+i)]++;
   return count;
}
  
/* removeDirtyChars takes two string as arguments: First
string (str)  is the one from where function removes dirty
characters. Second  string is the string which contain all
dirty characters which need to be removed  from first string */
char *removeDirtyChars(char *str, char *mask_str)
{
  int *count  = getCharCountArray(mask_str);
  int ip_ind  = 0, res_ind = 0;
  while (*(str + ip_ind))
  {
    char temp = *(str + ip_ind);
    if (count[temp] == 0)
    {
        *(str + res_ind) = *(str + ip_ind);
        res_ind++;
    }
    ip_ind++;
  }    
  
  /* After above step string is ngring. 
    Removing extra "iittg" after string*/
  *(str+res_ind) = '\0';    
  
  return str;
}
  
/* Driver program to test getCharCountArray*/
int main()
{
    char str[]         = "geeksforgeeks";
    char mask_str[]  = "mask";
    printf("%s", removeDirtyChars(str, mask_str));
    return 0;
}

chevron_right


Java

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program to remove duplicates, the order of
// characters is not maintained in this program
  
public class GFG 
{
    static final int NO_OF_CHARS = 256;
      
    /* Returns an array of size 256 containg count
       of characters in the passed char array */
    static int[] getCharCountArray(String str)
    {
       int count[] = new int[NO_OF_CHARS];
       for (int i = 0; i<str.length();  i++)
          count[str.charAt(i)]++;
         
       return count;
    }
      
    /* removeDirtyChars takes two string as arguments: First
    string (str)  is the one from where function removes dirty
    characters. Second  string is the string which contain all
    dirty characters which need to be removed  from first string */
    static String removeDirtyChars(String str, String mask_str)
    {
      int count[]  = getCharCountArray(mask_str);
      int ip_ind  = 0, res_ind = 0;
        
      char arr[] = str.toCharArray();
        
      while (ip_ind != arr.length)
      {
        char temp = arr[ip_ind];
        if(count[temp] == 0)
        {
            arr[res_ind] = arr[ip_ind];
            res_ind ++;
        }
            ip_ind++;
          
      }    
  
      str = new String(arr);
        
      /* After above step string is ngring. 
      Removing extra "iittg" after string*/
        
      return str.substring(0, res_ind);
        
    }
      
    // Driver Method
    public static void main(String[] args)
    {
        String str = "geeksforgeeks";
        String mask_str = "mask";
        System.out.println(removeDirtyChars(str, mask_str));
    }
}

chevron_right


Python

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python program to remove characters from first string which
# are present in the second string
NO_OF_CHARS = 256
  
# Utility function to convert from string to list
def toList(string):
    temp = []
    for x in string:
        temp.append(x)
    return temp
  
# Utility function to convert from list to string
def toString(List):
    return ''.join(List)
  
# Returns an array of size 256 containing count of characters
# in the passed char array
def getCharCountArray(string):
    count = [0] * NO_OF_CHARS
    for i in string:
        count[ord(i)] += 1
    return count
  
# removeDirtyChars takes two string as arguments: First
# string (str)  is the one from where function removes dirty
# characters. Second  string is the string which contain all
# dirty characters which need to be removed  from first string
def removeDirtyChars(string, mask_string):
    count = getCharCountArray(mask_string)
    ip_ind = 0
    res_ind = 0
    temp = ''
    str_list = toList(string)
  
    while ip_ind != len(str_list):
        temp = str_list[ip_ind]
        if count[ord(temp)] == 0:
            str_list[res_ind] = str_list[ip_ind]
            res_ind += 1
        ip_ind+=1
  
    # After above step string is ngring.
     # Removing extra "iittg" after string
    return toString(str_list[0:res_ind])
  
# Driver function to test the above functions
mask_string = "mask"
string = "geeksforgeeks"
print removeDirtyChars(string, mask_string)
  
# This code is contributed by Bhavya Jain

chevron_right


C#

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program to remove 
// duplicates, the order 
// of characters is not 
// maintained in this program
using System;
class GFG 
{
    static int NO_OF_CHARS = 256;
      
    /* Returns an array of size 
    256 containg count of 
    characters in the passed 
    char array */
    static int[] getCharCountArray(String str)
    {
        int[] count = new int[NO_OF_CHARS];
        for (int i = 0; i < str.Length; i++)
            count[str[i]]++;
              
        return count;
    }
      
    /* removeDirtyChars takes two
    string as arguments: First
    string (str) is the one from 
    where function removes dirty
    characters. Second string is 
    the string which contain all
    dirty characters which need 
    to be removed from first string */
    static String removeDirtyChars(String str, 
                                   String mask_str)
    {
    int[] count = getCharCountArray(mask_str);
    int ip_ind = 0, res_ind = 0;
      
    char[] arr = str.ToCharArray();
      
    while (ip_ind != arr.Length)
    {
        char temp = arr[ip_ind];
        if(count[temp] == 0)
        {
            arr[res_ind] = arr[ip_ind];
            res_ind ++;
        }
        ip_ind++;
          
    
  
    str = new String(arr);
      
    /* After above step string 
    is ngring. Removing extra 
    "iittg" after string*/
    return str.Substring(0, res_ind);
    }
      
    // Driver Code
    public static void Main()
    {
        String str = "geeksforgeeks";
        String mask_str = "mask";
        Console.WriteLine(removeDirtyChars(str, mask_str));
    }
}
  
// This code is contributed by mits

chevron_right



Output:

geeforgee

Time Complexity: O(m+n) Where m is the length of mask string and n is the length of the input string.

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



My Personal Notes arrow_drop_up

Improved By : Mithun Kumar



Article Tags :
Practice Tags :


Be the First to upvote.


Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.