Merge Sort(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         for(int i = 0; i < a.length; i++)
 8             a[i] = input.nextInt();
 9         divide(a, 0, a.length - 1);
10         
11         for(int i = 0; i < a.length; i++)
12             System.out.print(a[i] + " ");
13     }
14     
15     public static void divide(int[] a, int front, int rear)
16     {
17         if(front == rear)
18             return;
19         
20         int mid = front + (rear - front) / 2;
21         divide(a, mid + 1, rear);  //分割右半边
22         divide(a, front, mid);   //分割左半边
23         merge(a, front, mid, rear);   //进行归并
24     }
25     
26     public static void merge(int[] a, int front, int mid, int rear)
27     {
28         //先依次将排好序的元素放入b数组中(在放入b数组的过程中进行排序) 再将b数组元素依次放到a数组中
29         int[] b = new int[rear - front + 1];
30         int k = 0, i = front, j = mid + 1;
31         
32         while(i <= mid && j <= rear)
33         {
34             if(a[i] > a[j])
35                 b[k++] = a[j++];
36             else
37                 b[k++] = a[i++];
38         }
39         if(i > mid)
40             while(j <= rear)
41                 b[k++] = a[j++];
42         else
43             while(i <= mid)
44                 b[k++] = a[i++];
45         
46         for(int p = front, q = 0; p <= rear; p++, q++)
47             a[p] = b[q];
48     }