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++

// 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;
}

Java

// 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

Python3

# 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

C#

// 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

Output:

eeforee

Time Complexity: O(N)

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