按出现顺序打印具有质数频率的字符

给定一个仅包含小写字符的字符串str 。任务是按出现频率打印具有质数频率的字符。

请注意，具有质数频率的重复元素按其出现的次数打印多次。

例子：

Input: str = “geeksforgeeks” 
Output: gksgks 
 

Character	Frequency
‘g’	2
‘e’	4
‘k’	2
‘s’	2
‘f’	1
‘o’	1
‘r’	1

‘g’, ‘k’ and ‘s’ are the only characters with prime frequencies.
Input: str = “aeroplane” 
Output: aeae 

方法：创建一个频率数组，以存储给定字符串str的每个字符的频率。再次遍历字符串str，并使用Eratosthenes筛查该字符的频率是否为质数。

下面是上述方法的实现：

C++

// C++ implementation of the approach
#include 
using namespace std;
 
#define SIZE 26
 
// Function to create Sieve to check primes
void SieveOfEratosthenes(bool prime[], int p_size)
{
    // false here indicates
    // that it is not prime
    prime[0] = false;
    prime[1] = false;
 
    for (int p = 2; p * p <= p_size; p++) {
 
        // If prime[p] is not changed,
        // then it is a prime
        if (prime[p]) {
 
            // Update all multiples of p,
            // set them to non-prime
            for (int i = p * 2; i <= p_size; i += p)
                prime[i] = false;
        }
    }
}
 
// Function to print the prime frequency characters
// in the order of their occurrence
void printChar(string str, int n)
{
 
    bool prime[n + 1];
    memset(prime, true, sizeof(prime));
 
    // Function to create Sieve to check primes
    SieveOfEratosthenes(prime, str.length() + 1);
 
    // To store the frequency of each of
    // the character of the string
    int freq[SIZE];
 
    // Initialize all elements of freq[] to 0
    memset(freq, 0, sizeof(freq));
 
    // Update the frequency of each character
    for (int i = 0; i < n; i++)
        freq[str[i] - 'a']++;
 
    // Traverse str character by character
    for (int i = 0; i < n; i++) {
 
        // If frequency of current character is prime
        if (prime[freq[str[i] - 'a']]) {
            cout << str[i];
        }
    }
}
 
// Driver code
int main()
{
    string str = "geeksforgeeks";
    int n = str.length();
 
    printChar(str, n);
 
    return 0;
}

Java

// Java implementation of the approach
class GFG
{
     
static int SIZE = 26;
 
// Function to create Sieve to check primes
static void SieveOfEratosthenes(boolean []prime,
                                int p_size)
{
    // false here indicates
    // that it is not prime
    prime[0] = false;
    prime[1] = false;
 
    for (int p = 2; p * p <= p_size; p++)
    {
 
        // If prime[p] is not changed,
        // then it is a prime
        if (prime[p])
        {
 
            // Update all multiples of p,
            // set them to non-prime
            for (int i = p * 2; i < p_size; i += p)
                prime[i] = false;
        }
    }
}
 
// Function to print the prime frequency characters
// in the order of their occurrence
static void printChar(String str, int n)
{
    boolean []prime = new boolean[n + 1];
    for(int i = 0; i < n + 1; i++)
        prime[i] = true;
 
    // Function to create Sieve to check primes
    SieveOfEratosthenes(prime, str.length() + 1);
 
    // To store the frequency of each of
    // the character of the string
    int []freq = new int[SIZE];
 
    // Initialize all elements of freq[] to 0
    for(int i =0; i< SIZE; i++)
        freq[i]=0;
 
    // Update the frequency of each character
    for (int i = 0; i < n; i++)
        freq[str.charAt(i) - 'a']++;
 
    // Traverse str character by character
    for (int i = 0; i < n; i++)
    {
 
        // If frequency of current character is prime
        if (prime[freq[str.charAt(i) - 'a']])
        {
            System.out.print(str.charAt(i));
        }
    }
}
 
// Driver code
public static void main(String[] args)
{
    String str = "geeksforgeeks";
    int n = str.length();
 
    printChar(str, n);
}
}
 
// This code is contributed by PrinciRaj1992

Python 3

# Python 3 implementation of the approach
SIZE = 26
 
from math import sqrt
 
# Function to create Sieve to check primes
def SieveOfEratosthenes(prime, p_size):
     
    # false here indicates
    # that it is not prime
    prime[0] = False
    prime[1] = False
 
    for p in range(2, int(sqrt(p_size)), 1):
         
        # If prime[p] is not changed,
        # then it is a prime
        if (prime[p]):
             
            # Update all multiples of p,
            # set them to non-prime
            for i in range(p * 2, p_size, p):
                prime[i] = False
 
# Function to print the prime frequency characters
# in the order of their occurrence
def printChar(str, n):
    prime = [True for i in range(n + 1)]
 
    # Function to create Sieve to check primes
    SieveOfEratosthenes(prime, len(str) + 1)
 
    # To store the frequency of each of
    # the character of the string
    freq = [0 for i in range(SIZE)]
 
    # Update the frequency of each character
    for i in range(n):
        freq[ord(str[i]) - ord('a')] += 1
 
    # Traverse str character by character
    for i in range(n):
        # If frequency of current character is prime
        if (prime[freq[ord(str[i]) - ord('a')]]):
            print(str[i], end = "")
 
# Driver code
if __name__ == '__main__':
    str = "geeksforgeeks"
    n = len(str)
 
    printChar(str, n)
     
# This code is contributed by Surendra_Gangwar

C#

// C# implementation of the approach
using System;
 
class GFG
{
    static int SIZE = 26;
 
    // Function to create Sieve to check primes
    static void SieveOfEratosthenes(bool[] prime,
                                      int p_size)
    {
        // false here indicates
        // that it is not prime
        prime[0] = false;
        prime[1] = false;
 
        for (int p = 2; p * p <= p_size; p++)
        {
            // If prime[p] is not changed,
            // then it is a prime
            if (prime[p])
            {
                // Update all multiples of p,
                // set them to non-prime
                for (int i = p * 2;
                         i < p_size; i += p)
                    prime[i] = false;
            }
        }
    }
 
    // Function to print the prime frequency characters
    // in the order of their occurrence
    static void printChar(string str, int n)
    {
        bool[] prime = new bool[n + 1];
        for (int i = 0; i < n + 1; i++)
            prime[i] = true;
 
        // Function to create Sieve to check primes
        SieveOfEratosthenes(prime, str.Length + 1);
 
        // To store the frequency of each of
        // the character of the string
        int[] freq = new int[SIZE];
 
        // Initialize all elements of freq[] to 0
        for (int i = 0; i < SIZE; i++)
            freq[i] = 0;
 
        // Update the frequency of each character
        for (int i = 0; i < n; i++)
            freq[str[i] - 'a']++;
 
        // Traverse str character by character
        for (int i = 0; i < n; i++)
        {
 
            // If frequency of current character is prime
            if (prime[freq[str[i] - 'a']])
            {
                Console.Write(str[i]);
            }
        }
    }
 
    // Driver code
    public static void Main(String[] args)
    {
        String str = "geeksforgeeks";
        int n = str.Length;
 
        printChar(str, n);
    }
}
 
// This code is contibuted by
// sanjeev2552

输出

gksgks

方法2：使用内置函数：

方法：

我们将扫描字符串并使用内置的Counter()函数计算所有字符的出现次数，然后遍历字符串并检查出现的次数是否为质数，然后打印出来。

注意：此方法适用于所有类型的字符

下面是上述方法的实现：

Python3

# Python code for the above approach
 
# importing Counter function
from collections import Counter
import math
 
# Function to check primes
def prime(n):
    if n <= 1:
        return False
    max_div = math.floor(math.sqrt(n))
    for i in range(2, 1 + max_div):
        if n % i == 0:
            return False
    return True
 
 
def checkString(s):
 
    # Counting the frequency of all
    # character using Counter function
    freq = Counter(s)
 
    # Traversing string
    for i in range(len(s)):
        if prime(freq[s[i]]):
            print(s[i], end="")
 
 
# Driver code
s = "geeksforgeeks"
# passing string to checkString function
checkString(s)
 
# This code is contributed by vikkycirus

C＃

// C# code for the above approach
using System;
using System.Collections.Generic;
 
class GFG{
     
// Function to check primes
static bool prime(int n)
{
    if (n <= 1)
        return false;
         
    int max_div = (int)Math.Floor(Math.Sqrt(n));
    for(int i = 2; i < 1 + max_div; i++)
    {
        if (n % i == 0)
            return false;
    }
    return true;
}
 
static void checkString(string s)
{
     
    // Counting the frequency of all
    // character using Counter function
    Dictionary freq = new Dictionary();
    for(int i = 0; i < s.Length; i++)
    {
        if (!freq.ContainsKey(s[i]))
            freq[s[i]] = 0;
             
        freq[s[i]] += 1;
    }
     
    // Traversing string
    for(int i = 0; i < s.Length; i++)
    {
        if (prime(freq[s[i]]))
            Console.Write(s[i]);
    }
}
 
// Driver code
public static void Main()
{
    string s = "geeksforgeeks";
     
    // Passing string to checkString function
    checkString(s);
}
}
 
// This code is contributed by ukasp

输出

gksgks