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A few improvments of counting sort #409

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Merged
christianbender merged 2 commits into from
Apr 9, 2018
Merged

A few improvments of counting sort #409

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f564fa4
Added the counting sort method which uses stream API
nikitap492 Apr 6, 2018
205aec0
Changed the names of the counting sort methods
nikitap492 Apr 9, 2018
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134 changes: 75 additions & 59 deletions Sorts/CountingSort.java
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Original file line number Diff line number Diff line change
@@ -1,90 +1,106 @@
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;

/**
*
* @author Youssef Ali (https://github.com/youssefAli11997)
* @author Podshivalov Nikita (https://github.com/nikitap492)
*
*/

class CountingSort {

/**
* This method implements the Generic Counting Sort
*
* @param array The array to be sorted
* @param last The count of total number of elements in array
* Sorts the array in increasing order
* It uses array elements as keys in the frequency map
* @param list The list to be sorted
*
* Sorts the list in increasing order
* The method uses list elements as keys in the frequency map
**/

public static <T extends Comparable<T>> void CS(T[] array, int last) {

Map<T, Integer> frequency = new TreeMap<T, Integer>();
// The final output array
ArrayList<T> sortedArray = new ArrayList<T>();

// Counting the frequency of @param array elements
for(T t : array) {
try{
frequency.put(t, frequency.get(t)+1);
}catch(Exception e){ // new entry
frequency.put(t, 1);
}
}

// Filling the sortedArray
for(Map.Entry<T, Integer> element : frequency.entrySet()) {
for(int j=0; j<element.getValue(); j++)
public static <T extends Comparable<T>> List<T> countingSort(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());
}
}

for(int i=0; i<array.length; i++){
array[i] = sortedArray.get(i);
}

return sortedArray;
}


/**
* Stream Counting Sort
* The same as method {@link CountingSort#countingSort(List)} but this method uses stream API
*
* @param list The list to be sorted
*
**/
public static <T extends Comparable<T>> List<T> streamCountingSort(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
Integer[] arr1 = {4,23,6,78,1,54,231,9,12};
int last = arr1.length;

System.out.println("Before Sorting:");
for (int i=0;i<arr1.length;i++) {
System.out.print(arr1[i] + " ");
}
System.out.println();
List<Integer> unsortedInts = Stream.of(4, 23, 6, 78, 1, 54, 23, 1, 9, 231, 9, 12).collect(toList());

CS(arr1, last);
System.out.println("Before Sorting:");
printList(unsortedInts);

// Output => 1 4 6 9 12 23 54 78 231
// Output => 1 1 4 6 9 9 12 23 23 54 78 231
System.out.println("After Sorting:");
for (int i=0;i<arr1.length;i++) {
System.out.print(arr1[i] + " ");
}
System.out.println();

System.out.println("------------------------------");

printList(countingSort(unsortedInts));
System.out.println("After Sorting By Streams:");
printList(streamCountingSort(unsortedInts));

System.out.println("\n------------------------------\n");

// String Input
String[] array1 = {"c", "a", "e", "b","d"};
last = array1.length;

System.out.println("Before Sorting:");
for (int i=0;i<array1.length;i++) {
System.out.print(array1[i] + " ");
}
System.out.println();
List<String> unsortedStrings = Stream.of("c", "a", "e", "b","d", "a", "f", "g", "c").collect(toList());

CS(array1, last);
System.out.println("Before Sorting:");
printList(unsortedStrings);

//Output => a b c d e
//Output => a a b c c d e f g
System.out.println("After Sorting:");
for(int i=0; i<last; i++) {
System.out.print(array1[i]+" ");
}

printList(countingSort(unsortedStrings));

System.out.println("After Sorting By Streams:");
printList(streamCountingSort(unsortedStrings));

}

/**
* Just print list
* @param toPrint - a list which should be printed
*/
private static void printList(List<?> toPrint){
toPrint.stream()
.map(Object::toString)
.map(str -> str + " ")
.forEach(System.out::print);

System.out.println();
}
}
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