JavaAlgorithms/Sorts/TreeSort.java

package Sorts;

import static Sorts.SortUtils.print;

import java.util.List;

/**
 * <h1> Implementation of the Tree Sort algorithm</h1>
 *
 * <p>
 * Tree Sort: A sorting algorithm which constructs a Binary Search Tree
 * using the unsorted data and then outputs the data by inorder traversal
 * of the tree.
 *
 * Reference: https://en.wikipedia.org/wiki/Tree_sort
 * </p>
 *
 * @author Madhur Panwar (https://github.com/mdrpanwar)
 */
public class TreeSort implements SortAlgorithm {

  @Override
  public <T extends Comparable<T>> T[] sort(T[] unsortedArray) {
    return doTreeSortArray(unsortedArray);
  }

  @Override
  public <T extends Comparable<T>> List<T> sort(List<T> unsortedList) {
    return doTreeSortList(unsortedList);
  }

  private <T extends Comparable<T>> T[] doTreeSortArray(T[] unsortedArray) {
    // create a generic BST tree
    DataStructures.Trees.BSTRecursiveGeneric<T> tree = new DataStructures.Trees.BSTRecursiveGeneric<T>();

    // add all elements to the tree
    for(T element: unsortedArray) {
      tree.add(element);
    }

    // get the sorted list by inorder traversal of the tree
    List<T> sortedList = tree.inorderSort();

    // add the elements back to the initial array
    int i = 0;
    for(T element: sortedList) {
      unsortedArray[i++] = element;
    }

    // return the array
    return unsortedArray;
  }

  private <T extends Comparable<T>> List<T> doTreeSortList(List<T> unsortedList) {
    // create a generic BST tree
    DataStructures.Trees.BSTRecursiveGeneric<T> tree = new DataStructures.Trees.BSTRecursiveGeneric<T>();

    // add all elements to the tree
    for(T element: unsortedList) {
      tree.add(element);
    }

    // get the sorted list by inorder traversal of the tree and return it
    return tree.inorderSort();
  }

  public static void main(String[] args) {
    TreeSort treeSort = new TreeSort();

    // ==== Integer Array =======
    System.out.println("Testing for Integer Array....");
    Integer[] a = { 3, -7, 45, 1, 343, -5, 2, 9 };
    System.out.print(String.format("%-10s", "unsorted: "));
    print(a);
    a = treeSort.sort(a);
    System.out.print(String.format("%-10s", "sorted: "));
    print(a);
    System.out.println();

    // ==== Integer List =======
    System.out.println("Testing for Integer List....");
    List<Integer> intList = List.of(3, -7, 45, 1, 343, -5, 2, 9);
    System.out.print(String.format("%-10s", "unsorted: "));
    print(intList);
    intList = treeSort.sort(intList);
    System.out.print(String.format("%-10s", "sorted: "));
    print(intList);
    System.out.println();


    // ==== String Array =======
    System.out.println("Testing for String Array....");
    String[] b = { "banana", "berry", "orange", "grape", "peach", "cherry", "apple", "pineapple" };
    System.out.print(String.format("%-10s", "unsorted: "));
    print(b);
    b = treeSort.sort(b);
    System.out.print(String.format("%-10s", "sorted: "));
    print(b);
    System.out.println();

    // ==== String List =======
    System.out.println("Testing for String List....");
    List<String> stringList = List.of("banana", "berry", "orange", "grape", "peach", "cherry", "apple", "pineapple");
    System.out.print(String.format("%-10s", "unsorted: "));
    print(stringList);
    stringList = treeSort.sort(stringList);
    System.out.print(String.format("%-10s", "sorted: "));
    print(stringList);

  }

}