Remove characters from a String that appears exactly K times

Given a string of lowercase letters str of length N, the task is to reduce it by removing the characters which appear exactly K times in the string.

Examples:

Input: str = “geeksforgeeks”, K = 2
Output: eeforee

Input: str = “geeksforgeeks”, K = 4
Output: gksforgks

Approach:



  • Create a hash table of size 26, where 0th index represents ‘a’ and 1st index represent ‘b’ and so on.
  • Initialize the hash table to zero.
  • Iterate through the string and increment the frequency of each character(s[i]) in the hash table
  • Now, once again traverse through the string and append the characters, with frequency K, in the new string.

Below is the implementation of the above approach:

C++

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// C++ program to remove characters from
// a String that appears exactly K times
  
#include <bits/stdc++.h>
using namespace std;
  
const int MAX_CHAR = 26;
  
// Function to reduce the string by
// removing the characters which
// appears exactly k times
string removeChars(char arr[], int k)
{
    // Hash table initialised to 0
    int hash[MAX_CHAR] = { 0 };
  
    // Increment the frequency
    // of the character
    int n = strlen(arr);
    for (int i = 0; i < n; ++i)
        hash[arr[i] - 'a']++;
  
    // To store answer
    string ans = "";
  
    // Next index in reduced string
    int index = 0;
    for (int i = 0; i < n; ++i) {
  
        // Append the characters which
        // appears exactly k times
        if (hash[arr[i] - 'a'] != k) {
            ans += arr[i];
        }
    }
  
    return ans;
}
  
// Driver code
int main()
{
    char str[] = "geeksforgeeks";
    int k = 2;
  
    // Function call
    cout << removeChars(str, k);
  
    return 0;
}

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Java

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// Java program to remove characters from
// a String that appears exactly K times
import java.util.*;
  
class GFG{
   
static int MAX_CHAR = 26;
   
// Function to reduce the String by
// removing the characters which
// appears exactly k times
static String removeChars(char arr[], int k)
{
    // Hash table initialised to 0
    int []hash = new int[MAX_CHAR];
   
    // Increment the frequency
    // of the character
    int n = arr.length;
    for (int i = 0; i < n; ++i)
        hash[arr[i] - 'a']++;
   
    // To store answer
    String ans = "";
  
    for (int i = 0; i < n; ++i) {
   
        // Append the characters which
        // appears exactly k times
        if (hash[arr[i] - 'a'] != k) {
            ans += arr[i];
        }
    }
   
    return ans;
}
   
// Driver code
public static void main(String[] args)
{
    char str[] = "geeksforgeeks".toCharArray();
    int k = 2;
   
    // Function call
    System.out.print(removeChars(str, k));
}
}
  
// This code is contributed by 29AjayKumar

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Python3

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# Python 3 program to remove characters from
# a String that appears exactly K times
  
MAX_CHAR = 26
  
# Function to reduce the string by
# removing the characters which
# appears exactly k times
def removeChars(arr, k):
  
    # Hash table initialised to 0
    hash = [0]*MAX_CHAR
  
    # Increment the frequency
    # of the character
    n = len(arr)
    for i in range( n):
        hash[ord(arr[i]) - ord('a')] += 1
  
    # To store answer
    ans = ""
  
    # Next index in reduced string
    index = 0
    for i in range(n):
  
        # Append the characters which
        # appears exactly k times
        if (hash[ord(arr[i]) - ord('a')] != k):
            ans += arr[i]
          
    return ans
  
# Driver code
if __name__ =="__main__":
    str = "geeksforgeeks"
    k = 2
  
    # Function call
    print(removeChars(str, k))
  
# This code is contributed by chitranayal

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C#

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// C# program to remove characters from
// a String that appears exactly K times
using System;
  
class GFG{
    
static int MAX_CHAR = 26;
    
// Function to reduce the String by
// removing the characters which
// appears exactly k times
static String removeChars(char []arr, int k)
{
    // Hash table initialised to 0
    int []hash = new int[MAX_CHAR];
    
    // Increment the frequency
    // of the character
    int n = arr.Length;
    for (int i = 0; i < n; ++i)
        hash[arr[i] - 'a']++;
    
    // To store answer
    String ans = "";
   
    for (int i = 0; i < n; ++i) {
    
        // Append the characters which
        // appears exactly k times
        if (hash[arr[i] - 'a'] != k) {
            ans += arr[i];
        }
    }
    
    return ans;
}
    
// Driver code
public static void Main(String[] args)
{
    char []str = "geeksforgeeks".ToCharArray();
    int k = 2;
    
    // Function call
    Console.Write(removeChars(str, k));
}
}
  
// This code is contributed by 29AjayKumar

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Output:

eeforee

Time Complexity: O(N)

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Improved By : 29AjayKumar, chitranayal

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