Counting Sort Algorithm
Bucket sort may be used for many of the same tasks as counting sort, with a like time analysis; however, compared to counting sort, bucket sort necessitates associated lists, dynamic arrays or a large amount of preallocated memory to keep the sets of items within each bucket, whereas counting sort instead stores a individual number (the count of items) per bucket. Because counting sort uses key values as indexes into an array, it is not a comparison sort, and the Ω(n log N) Although radix sorting itself dates back far longer,
counting sort, and its application to radix sorting, were both invented by Harold H. Seward in 1954.
package Sorts;
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;
import static Sorts.SortUtils.print;
/**
* @author Youssef Ali (https://github.com/youssefAli11997)
* @author Podshivalov Nikita (https://github.com/nikitap492)
*/
class CountingSort implements SortAlgorithm {
@Override
public <T extends Comparable<T>> T[] sort(T[] unsorted) {
return sort(Arrays.asList(unsorted)).toArray(unsorted);
}
/**
* This method implements the Generic Counting Sort
*
* @param list The list to be sorted
* <p>
* Sorts the list in increasing order
* The method uses list elements as keys in the frequency map
**/
@Override
public <T extends Comparable<T>> List<T> sort(List<T> list) {
Map<T, Integer> frequency = new TreeMap<>();
// The final output array
List<T> sortedArray = new ArrayList<>(list.size());
// Counting the frequency of @param array elements
list.forEach(v -> frequency.put(v, frequency.getOrDefault(v, 0) + 1));
// Filling the sortedArray
for (Map.Entry<T, Integer> element : frequency.entrySet()) {
for (int j = 0; j < element.getValue(); j++) {
sortedArray.add(element.getKey());
}
}
return sortedArray;
}
/**
* Stream Counting Sort
* The same as method {@link CountingSort#sort(List)} } but this method uses stream API
*
* @param list The list to be sorted
**/
private static <T extends Comparable<T>> List<T> streamSort(List<T> list) {
return list.stream()
.collect(toMap(k -> k, v -> 1, (v1, v2) -> v1 + v2, TreeMap::new))
.entrySet()
.stream()
.flatMap(entry -> IntStream.rangeClosed(1, entry.getValue()).mapToObj(t -> entry.getKey()))
.collect(toList());
}
// Driver Program
public static void main(String[] args) {
// Integer Input
List<Integer> unsortedInts = Stream.of(4, 23, 6, 78, 1, 54, 23, 1, 9, 231, 9, 12).collect(toList());
CountingSort countingSort = new CountingSort();
System.out.println("Before Sorting:");
print(unsortedInts);
// Output => 1 1 4 6 9 9 12 23 23 54 78 231
System.out.println("After Sorting:");
print(countingSort.sort(unsortedInts));
System.out.println("After Sorting By Streams:");
print(streamSort(unsortedInts));
System.out.println("\n------------------------------\n");
// String Input
List<String> unsortedStrings = Stream.of("c", "a", "e", "b", "d", "a", "f", "g", "c").collect(toList());
System.out.println("Before Sorting:");
print(unsortedStrings);
//Output => a a b c c d e f g
System.out.println("After Sorting:");
print(countingSort.sort(unsortedStrings));
System.out.println("After Sorting By Streams:");
print(streamSort(unsortedStrings));
}
}
