归并排序思想

 1 //归并排序
 2 @Test
 3 public void mergeSort(){
 4     
 5     int arr[] = {100,7,9,4,1,6,3,10,5};
 6         
 7     int[] result = sort(arr, 0, arr.length-1);
 8     
 9     for(int i=0;i<result.length;i++){
10         System.out.print(result[i] + " ");
11     }
12 }
13 
14 public int[] sort(int arr[],int startIndex, int endIndex){
15     if(startIndex >= endIndex){
16         return new int[] {arr[endIndex]};
17     }
18     int midIndex = (startIndex+endIndex)/2;
19     int[] left = sort(arr, startIndex, midIndex);
20     int[] right = sort(arr, midIndex+1, endIndex);
21     return merge(left, right);
22 }
23 
24 public int[] merge(int[] left, int[] right){
25     int L_len = left.length, R_len = right.length;
26     int i=0,j=0,k=0;
27     int[] temp = new int[L_len + R_len];
28     
29     //将左右两边的子数组中的元素进行比较
30     while(i < L_len && j < R_len){
31         if(left[i] <= right[j]){
32             temp[k++] = left[i++];
33         }else{
34             temp[k++] = right[j++];
35         }
36     }
37     
38     //将子数组中剩余的元素放入排序数组的后面，下面的两个循环只会执行一个
39     while(i < L_len){
40         temp[k++] = left[i++];
41     }
42     
43     while(j < R_len){
44         temp[k++] = right[j++];
45     }
46     
47     return temp;
48 }