SortArrayIncreasingFrequency.java

package Leetcode;

import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;

/**
 * @author kalpak
 *
 * Given an array of integers nums, sort the array in increasing order based on the frequency of the values.
 * If multiple values have the same frequency, sort them in decreasing order.
 *
 * Return the sorted array.
 *
 *
 * Example 1:
 * Input: nums = [1,1,2,2,2,3]
 * Output: [3,1,1,2,2,2]
 * Explanation: '3' has a frequency of 1, '1' has a frequency of 2, and '2' has a frequency of 3.
 *
 * Example 2:
 * Input: nums = [2,3,1,3,2]
 * Output: [1,3,3,2,2]
 * Explanation: '2' and '3' both have a frequency of 2, so they are sorted in decreasing order.
 *
 * Example 3:
 * Input: nums = [-1,1,-6,4,5,-6,1,4,1]
 * Output: [5,-1,4,4,-6,-6,1,1,1]
 *
 * Constraints:
 *
 * 1 <= nums.length <= 100
 * -100 <= nums[i] <= 100
 */

public class SortArrayIncreasingFrequency {
 public static int[] frequencySort(int[] nums) {
 int[] result = new int[nums.length];
 int idx = 0;
 Map<Integer, Integer> map = new HashMap<>();
 PriorityQueue<Integer> minHeap = new PriorityQueue<>((a, b) -> (map.get(a) == map.get(b)) ? b - a : map.get(a) - map.get(b));

 for(int i : nums) {
 map.put(i, map.getOrDefault(i, 0) + 1);
 }

 for(int key : map.keySet())
 minHeap.offer(key);

 while(!minHeap.isEmpty()) {
 int temp = minHeap.poll();
 for(int i = map.get(temp); i > 0; i--)
 result[idx++] = temp;
 }

 return result;
 }

 public static void printArray(int[] nums) {
 for(int i : nums)
 System.out.print(i + " ");

 System.out.println();
 }

 public static void main(String[] args) {
 int[] arr = new int[]{1,1,2,2,2,3};
 printArray(frequencySort(arr));

 arr = new int[]{-1,1,-6,4,5,-6,1,4,1};
 printArray(frequencySort(arr));
 }
}