bharathi bharathi - 2 years ago 173
Java Question

Sort array based on count of occurrences in ascending order

How can I arrange the elements in an array based on the number of occurrences of that value in ascending order in java.

This is what I've tried:

int a[]={0,0,0,1,3,3,2,1,3,5,6,0};
int b=a.length;
for(int i=0;i<b;i++) {
for(int j=0;j<i;j++) {
int temp;
if( a[j]>a[i]) {

for(int r=0;r<a.length;r++) {

Edd Edd
Answer Source

Here's one approach to start you off could be based on the idea of keeping a count of how many times each integer in the initial array has occurred in a map. Once all the numbers have been counted, sort the map by order of ascending value, and then print the output of the map:

import java.util.ArrayList;
import java.util.HashMap;
import java.util.TreeMap;

public class SortCount {
    public static void main(String[] args) {
        int nums[] = {0,0,0,1,3,3,2,1,3,5,6,0};
        HashMap<Integer,Integer> counts = new HashMap<Integer,Integer>();

        for(int i = 0; i < nums.length; i++) {
                Integer c = counts.get(nums[i]) + 1;
                counts.put(nums[i], c);
            else {

        ValueComparator<Integer,Integer> bvc = new ValueComparator<Integer,Integer>(counts);
        TreeMap<Integer,Integer> sortedMap = new TreeMap<Integer,Integer>(bvc);

        ArrayList<Integer> output = new ArrayList<Integer>();
        for(Integer i : sortedMap.keySet()) {
            for(int c = 0; c < sortedMap.get(i); c++) {


Which uses a Comparator class to compare the values in a Map:

import java.util.Comparator;
import java.util.Map;

public class ValueComparator<T1,T2 extends Comparable<T2>> implements Comparator<T1> {
    Map<T1,T2> base;
    public ValueComparator(Map<T1,T2> base) {
        this.base = base;

    public int compare(T1 k1, T1 k2) {
        T2 val1 = base.get(k1);
        T2 val2 = base.get(k2);

        return val1.compareTo(val2);
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