Java/Sorts/CountingSort.java at master · java66liu/Java · GitHub

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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));

}

Java/Sorts/CountingSort.java at master · java66liu/Java · GitHub

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