【排序】归并排序

import java.util.Arrays;
import java.util.Random;

public class MergeSort {

    public static void main(String args[]) {
        int[] array = fillArray();
        split(array, 0, array.length - 1);
        System.out.println(Arrays.toString(array));
    }

    private static int[] fillArray() {
        Random random = new Random();
        int[] array = new int[100];
        for (int i = 0; i < 100; i++) {
            array[i] = random.nextInt(1000);
        }
        return array;
    }

    public static void split(int[] array, int left, int right) {
        if (left >= right) {
            return;
        }

        int mid = (left + right) / 2;
        split(array, left, mid);
        split(array, mid + 1, right);
        merge(array, left, mid, right);
    }

    private static void merge(int[] array, int left, int mid, int right) {
        int len = right - left + 1;
        int[] tmp = new int[len];

        int i = left;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= right) {
            if (array[i] <= array[j]) {
                tmp[k++] = array[i++];
            } else {
                tmp[k++] = array[j++];
            }
        }

        while (i <= mid) {
            tmp[k++] = array[i++];
        }

        while (j <= right) {
            tmp[k++] = array[j++];
        }

        int p = left;
        int q = 0;
        while (q < k) {
            array[p++] = tmp[q++];
        }
    }

}

• 时间复杂度：O(nlog(n))
• 空间复杂度：O(log(n))