Java ShellSort

Java ShellSort

/**
 * <html>
 * <body>
 *  <P> Copyright 1994-2018 JasonInternational </p>
 *  <p> All rights reserved.</p>
 *  <p> Created on 2018年4月10日 </p>
 *  <p> Created by Jason</p>
 *  </body>
 * </html>
 */
package cn.ucaner.algorithm.sorts;

import java.util.ArrayList;
import java.util.List;

/**
 * Shellsort, also known as Shell sort or Shell's method, is an in-place
 * comparison sort. It generalizes an exchanging sort, such as insertion or
 * bubble sort, by starting the comparison and exchange of elements with
 * elements that are far apart before finishing with neighboring elements.
 * Starting with far apart elements can move some out-of-place elements into
 * position faster than a simple nearest neighbor exchange. 
 * <p>
 * Family: Exchanging.<br>
 * Space: In-place.<br>
 * Stable: False.<br>
 * <p>
 * Average case = depends on the gap<br>
 * Worst case = O(n * log^2 n)<br>
 * Best case = O(n)<br>
 * <p>
 * @see <a href="https://en.wikipedia.org/wiki/Shell_sort">Shell Sort (Wikipedia)</a>
 * <br>
 * @author Justin Wetherell <phishman3579@gmail.com>
 */
public class ShellSort<T extends Comparable<T>> {

    private ShellSort() { }

    public static <T extends Comparable<T>> T[] sort(int[] shells, T[] unsorted) {
        for (int gap : shells) {
            // Allocate arrays
            List<List<T>> subarrays = new ArrayList<List<T>>(gap);
            for (int i = 0; i < gap; i++) {
                subarrays.add(new ArrayList<T>(10));
            }
            // Populate sub-arrays
            int i = 0;
            int length = unsorted.length;
            while (i < length) {
                for (int j = 0; j < gap; j++) {
                    if (i >= length)
                        continue;
                    T v = unsorted[i++];
                    List<T> list = subarrays.get(j);
                    list.add(v);
                }
            }
            // Sort all sub-arrays
            sortSubarrays(subarrays);
            // Push the sub-arrays into the int array
            int k = 0;
            int iter = 0;
            while (k < length) {
                for (int j = 0; j < gap; j++) {
                    if (k >= length)
                        continue;
                    unsorted[k++] = subarrays.get(j).get(iter);
                }
                iter++;
            }
        }
        return unsorted;
    }

    private static <T extends Comparable<T>> void sortSubarrays(List<List<T>> lists) {
        for (List<T> list : lists) {
            sort(list);
        }
    }

    /**
     * Insertion sort
     * 
     * @param list
     *            List to be sorted.
     */
    private static <T extends Comparable<T>> void sort(List<T> list) {
        int size = list.size();
        for (int i = 1; i < size; i++) {
            for (int j = i; j > 0; j--) {
                T a = list.get(j);
                T b = list.get(j - 1);
                if (a.compareTo(b) < 0) {
                    list.set(j - 1, a);
                    list.set(j, b);
                } else {
                    break;
                }
            }
        }
    }
}

　　

posted @ 2018-06-29 14:15  安以北往南  阅读(412)  评论(0)  编辑  收藏  举报