Counting Sort Implementation

Imagine you have an array like this (note that the array has duplicates, and includes 0 and k):

a = [ 4, 64, 200, 42, 56, 22, 1, 64, 0, 161, 200, 0, 42 ]

 

What you know about this array is

Values are integers

Values are non-negative and less than some number, for example:

0 <= value <= k, where k is an integer

To start, can you please write some code to sort this array using any algorithm you want and not using the library functions. Let’s assume there are no space/time requirements. This part of the coding interview is not about the algorithms, our goal is to write some code and get it running.

 

public void bucketSort(int[] arr) {
        if (arr == null || arr.length < 1) return;
        Map<Integer, Integer> itemToCountMapping = new HashMap<>();
        int min = arr[0];
        int max = arr[0];

        for (int value : arr) {
            min = Math.min(min, value);
            max = Math.max(max, value);
            itemToCountMapping.put(value, itemToCountMapping.getOrDefault(value, 0) + 1);
        }
        
        int index = 0;
        for (int i = min; i <= max; i++) {
            int count = itemToCountMapping.getOrDefault(i, 0);
            for (int j = 1; j <= count; j++) {
                arr[index] = i;
                index++;
            }
        }
    }