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Add Dutch National Flag Sort (#3025)

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Co-authored-by: Antonia Strack <antonia.strack@thm.mni.de>
Co-authored-by: Andrii Siriak <siryaka@gmail.com>
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BranAndSceolan 2022-04-25 16:02:15 +02:00 committed by GitHub
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commit dfdce96c6e
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44
src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java Normal file
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package com.thealgorithms.sorts;
/**
* The Dutch National Flag Sort sorts a sequence of values into three permutations which are defined by a value given
* as the indented middle.
* First permutation: values less than middle.
* Second permutation: values equal middle.
* Third permutation: values greater than middle.
* If no indented middle is given, this implementation will use a value from the given Array.
* This value is the one positioned in the arrays' middle if the arrays' length is odd.
* If the arrays' length is even, the value left to the middle will be used.
* More information and Pseudocode: https://en.wikipedia.org/wiki/Dutch_national_flag_problem
*/
public class DutchNationalFlagSort implements SortAlgorithm {
@Override
public <T extends Comparable<T>> T[] sort(T[] unsorted) {
return dutch_national_flag_sort(unsorted, unsorted[(int) Math.ceil((unsorted.length)/2.0) -1]);
}
public <T extends Comparable<T>> T[] sort(T[] unsorted, T intendedMiddle) {
return dutch_national_flag_sort(unsorted, intendedMiddle);
}
private <T extends Comparable<T>> T[] dutch_national_flag_sort(T[] arr, T intendedMiddle){
int i = 0;
int j = 0;
int k = arr.length - 1;
while( j <= k){
if ( 0 > arr[j].compareTo(intendedMiddle)){
SortUtils.swap(arr, i, j);
j++;
i++;
} else if (0 < arr[j].compareTo(intendedMiddle)){
SortUtils.swap(arr, j, k);
k--;
} else {
j++;
}
}
return arr;
}
}

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src/test/java/com/thealgorithms/sorts/DutchNationalFlagSortTest.java Normal file
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package com.thealgorithms.sorts;
import org.junit.jupiter.api.Test;
import java.util.Arrays;
import static org.junit.jupiter.api.Assertions.*;
public class DutchNationalFlagSortTest {
@Test
/*
1 will be used as intended middle.
Partitions on the result array: [ smaller than 1 , equal 1, greater than 1]
*/
void DNFSTestOdd() {
Integer[] integers = {1, 3, 1, 4, 0};
Integer[] integersResult = {0, 1, 1, 4, 3};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(integers);
assertArrayEquals(integers, integersResult);
}
@Test
/*
3 will be used as intended middle.
Partitions on the result array: [ smaller than 3 , equal 3, greater than 3]
*/
void DNFSTestEven() {
Integer[] integers = {8, 1, 3, 1, 4, 0};
Integer[] integersResult = {0, 1, 1, 3, 4, 8};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(integers);
assertArrayEquals(integers, integersResult);
}
@Test
/*
"b" will be used as intended middle.
Partitions on the result array: [ smaller than b , equal b, greater than b]
*/
void DNFSTestEvenStrings() {
String[] strings = {"a", "d", "b", "s", "e", "e"};
String[] stringsResult = {"a", "b", "s", "e", "e", "d"};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(strings);
assertArrayEquals(strings, stringsResult);
}
@Test
/*
"b" will be used as intended middle.
Partitions on the result array: [ smaller than b , equal b, greater than b]
*/
void DNFSTestOddStrings() {
String[] strings = {"a", "d", "b", "s", "e"};
String[] stringsResult = {"a", "b", "s", "e", "d"};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(strings);
assertArrayEquals(strings, stringsResult);
}
@Test
/*
0 will be used as intended middle.
Partitions on the result array: [ smaller than 0 , equal 0, greater than 0]
*/
void DNFSTestOddMidGiven() {
Integer[] integers = {1, 3, 1, 4, 0};
Integer[] integersResult = {0, 1, 4, 3, 1};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(integers, 0);
assertArrayEquals(integers, integersResult);
}
@Test
/*
4 will be used as intended middle.
Partitions on the result array: [ smaller than 4 , equal 4, greater than 4]
*/
void DNFSTestEvenMidGiven() {
Integer[] integers = {8, 1, 3, 1, 4, 0};
Integer[] integersResult = {0, 1, 3, 1, 4, 8};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(integers, 4);
assertArrayEquals(integers, integersResult);
}
@Test
/*
"s" will be used as intended middle.
Partitions on the result array: [ smaller than s , equal s, greater than s]
*/
void DNFSTestEvenStringsMidGiven() {
String[] strings = {"a", "d", "b", "s", "e", "e"};
String[] stringsResult = {"a", "d", "b", "e", "e", "s"};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(strings, "s");
assertArrayEquals(strings, stringsResult);
}
@Test
/*
"e" will be used as intended middle.
Partitions on the result array: [ smaller than e , equal e, greater than e]
*/
void DNFSTestOddStringsMidGiven() {
String[] strings = {"a", "d", "b", "s", "e"};
String[] stringsResult = {"a", "d", "b", "e", "s"};
DutchNationalFlagSort dutchNationalFlagSort = new DutchNationalFlagSort();
dutchNationalFlagSort.sort(strings, "e");
assertArrayEquals(strings, stringsResult);
}
}