排序算法之归并排序

import static org.junit.Assert.*;



import java.util.Arrays;



import org.junit.Test;



public class SortAlgorithms {

/**

     * 归并排序算法

     * 

     * @param a

     * @return

     */

    static void mergeSort(int[] a, int start, int end) {

        if (start < end - 1) {

            int mid = (start + end) / 2;

            mergeSort(a, start, mid);

            mergeSort(a, mid, end);

            merge(a, start, mid, end);

        }

    }



    /**

     * 归并排序中将两个已经排序的序列合并

     * 

     * @param a

     * @param b

     * @return

     */

    protected static void merge(int[] n, int start, int mid, int end) {

        int[] l = Arrays.copyOfRange(n, start, mid);

        int[] r = Arrays.copyOfRange(n, mid, end);

        int i = 0;

        int j = 0;// j<mid-start

        int k = 0;// k<end-mid

        while (i < end - start) {

            if (j < mid - start & k < end - mid) {

                if (l[j] < r[k]) {

                    n[i + start] = l[j];

                    j++;

                } else {

                    n[i + start] = r[k];

                    k++;

                }

            } else if (k < end - mid) {

                n[i + start] = r[k];

                k++;

            } else if (j < mid - start) {

                n[i + start] = l[j];

                j++;

            }

            i++;

        }

    }



}