107 lines
3.2 KiB
Java
107 lines
3.2 KiB
Java
import java.util.ArrayList;
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import java.util.List;
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import java.util.Map;
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import java.util.TreeMap;
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import java.util.stream.IntStream;
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import java.util.stream.Stream;
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import static java.util.stream.Collectors.toList;
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import static java.util.stream.Collectors.toMap;
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/**
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*
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* @author Youssef Ali (https://github.com/youssefAli11997)
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* @author Podshivalov Nikita (https://github.com/nikitap492)
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*
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*/
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class CountingSort {
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/**
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* This method implements the Generic Counting Sort
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*
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* @param list The list to be sorted
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*
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* Sorts the list in increasing order
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* The method uses list elements as keys in the frequency map
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**/
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public static <T extends Comparable<T>> List<T> countingSort(List<T> list) {
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Map<T, Integer> frequency = new TreeMap<>();
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// The final output array
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List<T> sortedArray = new ArrayList<>(list.size());
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// Counting the frequency of @param array elements
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list.forEach(v -> frequency.put(v, frequency.getOrDefault(v, 0) + 1));
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// Filling the sortedArray
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for(Map.Entry<T, Integer> element : frequency.entrySet()) {
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for(int j=0; j<element.getValue(); j++){
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sortedArray.add(element.getKey());
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}
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}
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return sortedArray;
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}
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/**
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* Stream Counting Sort
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* The same as method {@link CountingSort#countingSort(List)} but this method uses stream API
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*
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* @param list The list to be sorted
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*
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**/
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public static <T extends Comparable<T>> List<T> streamCountingSort(List<T> list) {
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return list.stream()
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.collect(toMap(k -> k, v -> 1, (v1, v2) -> v1 + v2, TreeMap::new))
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.entrySet()
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.stream()
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.flatMap(entry -> IntStream.rangeClosed(1, entry.getValue()).mapToObj(t -> entry.getKey()))
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.collect(toList());
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}
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// Driver Program
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public static void main(String[] args) {
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// Integer Input
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List<Integer> unsortedInts = Stream.of(4, 23, 6, 78, 1, 54, 23, 1, 9, 231, 9, 12).collect(toList());
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System.out.println("Before Sorting:");
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printList(unsortedInts);
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// Output => 1 1 4 6 9 9 12 23 23 54 78 231
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System.out.println("After Sorting:");
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printList(countingSort(unsortedInts));
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System.out.println("After Sorting By Streams:");
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printList(streamCountingSort(unsortedInts));
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System.out.println("\n------------------------------\n");
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// String Input
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List<String> unsortedStrings = Stream.of("c", "a", "e", "b","d", "a", "f", "g", "c").collect(toList());
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System.out.println("Before Sorting:");
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printList(unsortedStrings);
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//Output => a a b c c d e f g
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System.out.println("After Sorting:");
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printList(countingSort(unsortedStrings));
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System.out.println("After Sorting By Streams:");
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printList(streamCountingSort(unsortedStrings));
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}
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/**
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* Just print list
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* @param toPrint - a list which should be printed
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*/
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private static void printList(List<?> toPrint){
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toPrint.stream()
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.map(Object::toString)
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.map(str -> str + " ")
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.forEach(System.out::print);
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System.out.println();
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}
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}
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