java算法----排序----（5）归并排序

package log;

import java.util.Arrays;

public class Test4 {

    /**
     * java算法---归并排序
     * 
     * @param args
     */
    public static void main(String[] args) {
        // 需要排序的数组
        int arr[] = { 49, 20, 36, 51, 18, 94, 61, 31, 50 };
        // 循环输出该数组内容
        System.out.println("排序之前：");
        for (int a : arr) {
            System.out.print(a + "	");
        }
        System.out.println();

        sort(arr, 0, arr.length - 1);
        // 循环输出该数组内容
        System.out.println("排序之后：");
        for (int a : arr) {
            System.out.print(a + "	");
        }
        System.out.println();

    }

    public static void merge(int[] list, int left, int center, int right) {
        int[] tempArr = new int[list.length];
        int mid = center + 1;
        int third = left;
        int temp = left;
        while (left <= center && mid <= right) {
            if (list[left] <= list[mid]) {
                tempArr[third++] = list[left++];
            } else {
                tempArr[third++] = list[mid++];
            }
        }
        while (mid <= right) {
            tempArr[third++] = list[mid++];
        }
        while (left <= center) {
            tempArr[third++] = list[left++];
        }
        while (temp <= right) {
            list[temp] = tempArr[temp++];
        }
        System.out.println(Arrays.toString(list));
    }

    public static void sort(int[] list, int left, int right) {
        if (left < right) {
            int center = (left + right) / 2;
            sort(list, left, center);
            sort(list, center + 1, right);
            merge(list, left, center, right);
        }
    }

}

下面是控制台的输出结果

归并排序是将两个或者两个以上有序表合并成一个新的有序表，即把带排序序列分为若干个子序列，每个子序列都是有序的。然后再把有序子序列合并为整体有序序列。