geeksforgeeks@ Sorting Elements of an Array by Frequency (Sort)

http://www.practice.geeksforgeeks.org/problem-page.php?pid=493

Sorting Elements of an Array by Frequency

Given an array of integers, sort the array according to frequency of elements. For example, if the input array is {2, 3, 2, 4, 5, 12, 2, 3, 3, 3, 12}, then modify the array to {3, 3, 3, 3, 2, 2, 2, 12, 12, 4, 5}.

If frequencies of two elements are same, print them in increasing order.

Input:

The first line of input contains an integer T denoting the number of test cases. The description of T test cases follows. The first line of each test case contains a single integer N denoting the size of array. The second line contains N space-separated integers A1, A2, ..., AN denoting the elements of the array.

Output:

Print each sorted array in a seperate line. For each array its numbers should be seperated by space.

Constraints:

1 ≤ T ≤ 70
30 ≤ N ≤ 130
1 ≤ A [ i ] ≤ 60

Example:

Input:

1
5
5 5 4 6 4

Output:

4 4 5 5 6

import java.util.*;
import java.lang.*;
import java.io.*;

class pair {
    public int freq;
    public int key;
    public pair(int f, int k) {
        super();
        this.freq = f;
        this.key = k;
    }
}

class cmp implements Comparator<pair> {

    public int compare(pair p1, pair p2) {
        if(p1.freq != p2.freq) {
            return p2.freq - p1.freq;
        } else {
            return p1.key - p2.key;
        }
    }
}

class GFG {

    public static void pln(Object[] ls) {
        for(int i=0; i<ls.length; ++i) {
            System.out.print(ls[i]);
        } System.out.println();
    }

    public static void func(int[] arr) {

        int n = arr.length;
        HashMap<Integer, Integer> mapping = new HashMap<Integer, Integer> ();

        for(int na: arr) {
            if(!mapping.containsKey(na)) {
                mapping.put(na, 0);
            }
            mapping.put(na, mapping.get(na) + 1);
        }

        TreeSet<pair> freqToKey = new TreeSet<pair> (new cmp());
        Iterator iter = mapping.entrySet().iterator();
        while(iter.hasNext()) {
            Map.Entry entry = (Map.Entry) iter.next();
            int key = (int) entry.getKey();
            int freq = (int) entry.getValue();
            pair p = new pair(freq, key);
            freqToKey.add(p);
        }

        Object[] ls = freqToKey.toArray();
        for(int i=0; i<ls.length; ++i) {
            pair p = (pair) ls[i];
            int freq = p.freq;
            int key = p.key;

            while(freq > 0) {
                --freq;
                System.out.print(key + " ");
            }
        } System.out.println();
    }

    public static void main (String[] args) {
        Scanner in = new Scanner(System.in);
        int times = in.nextInt();

        while(times > 0) {
            --times;

            int n = in.nextInt();
            int[] arr = new int[n];
            for(int i=0; i<n; ++i) {
                arr[i] = in.nextInt();
            }

            func(arr);
        }
    }
}