Insertion Sort 与 Merge Sort的性能比较(Java)

 1 　　 public static void main(String[] args)
 2     {
 3         Scanner input = new Scanner(System.in);
 4         int n = input.nextInt();
 5         int[] a = new int[n];
 6         
 7         //生成n个随机数
 8         for(int i = 0; i < n; i++)
 9             a[i] = (int)(Math.random() * 100);
10         
11         /*long start = System.currentTimeMillis();
12         InsertionSort(a);
13         long end = System.currentTimeMillis();*/
14         //100000个测试数据InsertionSort的排序时间约为2800ms
15             
16         /*System.out.println(Arrays.toString(a));
17         System.out.println(start);
18         System.out.println(end);
19         System.out.printf("The time is: %d", end - start);*/
20         
21         //获取当前时间(ms)
22         long start = System.currentTimeMillis();
23         divide(a, 0, a.length - 1);
24         long end = System.currentTimeMillis();
25         //100000000个测试数据MergeSort的排序时间约为12000ms 10000000个测试数据用时约为1200ms
26         //相对于平均时间复杂度O(n^2)的插入排序 随着测试数据数量级的增长 性能提升极大
27         
28         //System.out.println(Arrays.toString(a));
29         System.out.println(start);
30         System.out.println(end);
31         // end - start 即为排序算法运行的时间
32         System.out.println("The time is: " + (end - start));
33     }
34     
35     /*public static void InsertionSort(int[] a)
36     {
37         for(int i = 1; i < a.length; i++)
38         {
39             int key = a[i];
40             int j;
41             for(j = i - 1; j >= 0 && key < a[j]; j--)
42                 a[j + 1] = a[j];
43             a[j + 1] = key;
44         }
45     }*/
46     
47     public static void divide(int[] a, int front, int rear)
48     {
49         if(rear <= front)
50             return;
51         
52         int mid = front + (rear - front) / 2;
53         divide(a, mid + 1, rear);
54         divide(a, front, mid);
55         merge(a, front, mid, rear);
56     }
57     
58     public static void merge(int[] a, int front, int mid, int rear)
59     {
60         int[] b = new int[rear - front + 1];
61         int i = front, j = mid + 1, k = 0;
62         
63         while(i <= mid && j <= rear)
64             if(a[i] < a[j])
65                 b[k++] = a[i++];
66             else
67                 b[k++] = a[j++];
68         
69         if(i > mid)
70             while(j <= rear)
71                 b[k++] = a[j++];
72         else
73             while(i <= mid)
74                 b[k++] = a[i++];
75         
76         for(int t = 0, q = front; t < b.length; t++, ++q)
77             a[q] = b[t];
78     }