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Print numbers in descending order along with their frequencies
  • Last Updated : 18 Feb, 2020

Given an array arr, the task is to print the elements of the array in descending order along with their frequencies.

Examples:

Input: arr[] = {1, 3, 3, 3, 4, 4, 5}
Output: 5 occurs 1 times
4 occurs 2 times
3 occurs 3 times
1 occurs 1 times

Input: arr[] = {1, 1, 1, 2, 3, 4, 9, 9, 10}
Output: 10 occurs 1 times
9 occurs 2 times
4 occurs 1 times
3 occurs 1 times
2 occurs 1 times
1 occurs 3 times

Naive approach: Use some Data-Structure (e.g. multiset) which stores elements in decreasing order and then print the elements one by one with it’s count and then erase it from the Data-structure. The time complexity will be O(N log N) and the auxiliary space will be O(N) for the Data-structure used.



Below is the implementation of the above approach:




// C++ program to print the elements in
// descending along with their frequencies
#include <bits/stdc++.h>
using namespace std;
  
// Function to print the elements in descending
// along with their frequencies
void printElements(int a[], int n)
{
  
    // A multiset to store elements in decreasing order
    multiset<int, greater<int> > ms;
  
    // Insert elements in the multiset
    for (int i = 0; i < n; i++) {
        ms.insert(a[i]);
    }
  
    // Print the elements along with their frequencies
    while (!ms.empty()) {
  
        // Find the maximum element
        int maxel = *ms.begin();
  
        // Number of times it occurs
        int times = ms.count(maxel);
  
        cout << maxel << " occurs " << times << " times\n";
  
        // Erase the maxel
        ms.erase(maxel);
    }
}
  
// Driver Code
int main()
{
    int a[] = { 1, 1, 1, 2, 3, 4, 9, 9, 10 };
    int n = sizeof(a) / sizeof(a[0]);
    printElements(a, n);
    return 0;
}
Output:
10 occurs 1 times
9 occurs 2 times
4 occurs 1 times
3 occurs 1 times
2 occurs 1 times
1 occurs 3 times

Efficient Approach: Sort the array in descending order and then start printing the elements from the beginning along with their frequencies.

Below is the implementation of the above approach:

C++




// C++ program to print the elements in
// descending along with their frequencies
#include <bits/stdc++.h>
using namespace std;
  
// Function to print the elements in descending
// along with their frequencies
void printElements(int a[], int n)
{
  
    // Sorts the element in decreasing order
    sort(a, a + n, greater<int>());
    int cnt = 1;
  
    // traverse the array elements
    for (int i = 0; i < n - 1; i++) {
  
        // Prints the number and count
        if (a[i] != a[i + 1]) {
            cout << a[i] << " occurs " << cnt << " times\n";
            cnt = 1;
        }
        else
            cnt += 1;
    }
  
    // Prints the last step
    cout << a[n - 1] << " occurs " << cnt << " times\n";
}
  
// Driver Code
int main()
{
    int a[] = { 1, 1, 1, 2, 3, 4, 9, 9, 10 };
    int n = sizeof(a) / sizeof(a[0]);
  
    printElements(a, n);
    return 0;
}

Java




// Java program to print the elements in
// descending along with their frequencies
import java.util.*;
  
class GFG
{
  
// Function to print the elements in descending
// along with their frequencies
static void printElements(int a[], int n)
{
  
    // Sorts the element in decreasing order
    Arrays.sort(a);
    a = reverse(a);
    int cnt = 1;
  
    // traverse the array elements
    for (int i = 0; i < n - 1; i++) 
    {
  
        // Prints the number and count
        if (a[i] != a[i + 1])
        {
            System.out.print(a[i]+ " occurs " +
                            cnt + " times\n");
            cnt = 1;
        }
        else
            cnt += 1;
    }
  
    // Prints the last step
    System.out.print(a[n - 1]+ " occurs "
                    cnt + " times\n");
}
  
static int[] reverse(int a[])
{
    int i, n = a.length, t;
    for (i = 0; i < n / 2; i++)
    {
        t = a[i];
        a[i] = a[n - i - 1];
        a[n - i - 1] = t;
    }
    return a;
}
  
// Driver Code
public static void main(String[] args)
{
    int a[] = { 1, 1, 1, 2, 3, 4, 9, 9, 10 };
    int n = a.length;
  
    printElements(a, n);
}
}
  
// This code is contributed by PrinciRaj1992

Python3




# Python3 program to print the elements in 
# descending along with their frequencies 
  
# Function to print the elements in 
# descending along with their frequencies 
def printElements(a, n) :
  
    # Sorts the element in decreasing order 
    a.sort(reverse = True
    cnt = 1
  
    # traverse the array elements 
    for i in range(n - 1) :
  
        # Prints the number and count 
        if (a[i] != a[i + 1]) : 
            print(a[i], " occurs ", cnt, "times"
            cnt = 1
          
        else :
            cnt += 1
      
    # Prints the last step 
    print(a[n - 1], "occurs", cnt, "times"
  
# Driver Code 
if __name__ == "__main__" :
  
    a = [ 1, 1, 1, 2
          3, 4, 9, 9, 10
    n = len(a)
  
    printElements(a, n)
      
# This code is contributed by Ryuga

C#




// C# program to print the elements in
// descending along with their frequencies
using System;
  
class GFG
{
  
// Function to print the elements in descending
// along with their frequencies
static void printElements(int []a, int n)
{
  
    // Sorts the element in decreasing order
    Array.Sort(a);
    a = reverse(a);
    int cnt = 1;
  
    // traverse the array elements
    for (int i = 0; i < n - 1; i++) 
    {
  
        // Prints the number and count
        if (a[i] != a[i + 1])
        {
            Console.Write(a[i]+ " occurs " +
                            cnt + " times\n");
            cnt = 1;
        }
        else
            cnt += 1;
    }
  
    // Prints the last step
    Console.Write(a[n - 1]+ " occurs "
                    cnt + " times\n");
}
  
static int[] reverse(int []a)
{
    int i, n = a.Length, t;
    for (i = 0; i < n / 2; i++)
    {
        t = a[i];
        a[i] = a[n - i - 1];
        a[n - i - 1] = t;
    }
    return a;
}
  
// Driver Code
public static void Main(String[] args)
{
    int []a = { 1, 1, 1, 2, 3, 4, 9, 9, 10 };
    int n = a.Length;
  
    printElements(a, n);
}
}
  
// This code is contributed by PrinciRaj1992

PHP




<?php
// PHP program to print the elements in
// descending along with their frequencies
  
// Function to print the elements in 
// descending along with their frequencies
function printElements(&$a, $n)
{
  
    // Sorts the element in 
    // decreasing order
    rsort($a);
    $cnt = 1;
  
    // traverse the array elements
    for ($i = 0; $i < $n - 1; $i++) 
    {
  
        // Prints the number and count
        if ($a[$i] != $a[$i + 1]) 
        {
            echo ($a[$i]); 
            echo (" occurs " );
            echo $cnt ;
            echo (" times\n");
            $cnt = 1;
        }
        else
            $cnt += 1;
    }
  
    // Prints the last step
    echo ($a[$n - 1]); 
    echo (" occurs ");
    echo $cnt;
    echo (" times\n");
}
  
// Driver Code
$a = array(1, 1, 1, 2, 3,
           4, 9, 9, 10 );
$n = sizeof($a);
  
printElements($a, $n);
  
// This code is contributed
// by Shivi_Aggarwal
?>
Output:
10 occurs 1 times
9 occurs 2 times
4 occurs 1 times
3 occurs 1 times
2 occurs 1 times
1 occurs 3 times
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