JavaAlgorithms/Sorts/CycleSort.java

package Sorts;

import static Sorts.SortUtils.less;
import static Sorts.SortUtils.print;

/** @author Podshivalov Nikita (https://github.com/nikitap492) */
class CycleSort implements SortAlgorithm {

  @Override
  public <T extends Comparable<T>> T[] sort(T[] arr) {
    int n = arr.length;

    // traverse array elements
    for (int j = 0; j <= n - 2; j++) {
      // initialize item as starting point
      T item = arr[j];

      // Find position where we put the item.
      int pos = j;
      for (int i = j + 1; i < n; i++) if (less(arr[i], item)) pos++;

      // If item is already in correct position
      if (pos == j) continue;

      // ignore all duplicate elements
      while (item.compareTo(arr[pos]) == 0) pos += 1;

      // put the item to it's right position
      if (pos != j) {
        item = replace(arr, pos, item);
      }

      // Rotate rest of the cycle
      while (pos != j) {
        pos = j;

        // Find position where we put the element
        for (int i = j + 1; i < n; i++)
          if (less(arr[i], item)) {
            pos += 1;
          }

        // ignore all duplicate elements
        while (item.compareTo(arr[pos]) == 0) pos += 1;

        // put the item to it's right position
        if (item != arr[pos]) {
          item = replace(arr, pos, item);
        }
      }
    }

    return arr;
  }

  private <T extends Comparable<T>> T replace(T[] arr, int pos, T item) {
    T temp = item;
    item = arr[pos];
    arr[pos] = temp;
    return item;
  }

  public static void main(String[] args) {
    Integer arr[] = {4, 23, 6, 78, 1, 26, 11, 23, 0, -6, 3, 54, 231, 9, 12};
    CycleSort cycleSort = new CycleSort();
    cycleSort.sort(arr);

    System.out.println("After sort : ");
    print(arr);
  }
}