In this Kata, you will sort elements in an array by decreasing frequency of elements. If two elements have the same frequency, sort them by increasing value.
Solution.sortByFrequency(new int[]{2, 3, 5, 3, 7, 9, 5, 3, 7});
// Returns {3, 3, 3, 5, 5, 7, 7, 2, 9}
// We sort by highest frequency to lowest frequency.
// If two elements have same frequency, we sort by increasing value.
More examples in test cases.