归并排序

 1 void merge(int arr[], int l, int m,int r)
 2 {
 3     int i = 0, j = 0, k =l;
 4     int n1 = m - l + 1;        //左边步长
 5     int n2 = r - m;            //右边步长
 6     std::vector<int> vec_l(&arr[l], &arr[m+1]);
 7     std::vector<int> vec_r(&arr[m+1], &arr[r+1]);
 8     while (i < n1&&j < n2)
 9     {
10         if (vec_l[i] <= vec_r[j])
11         {
12             arr[k] = vec_l[i];
13             i++;
14         }
15         else
16         {
17             arr[k] = vec_r[j];
18             j++;
19         }
20         k++;
21     }
22         while (i<n1)
23         {
24             arr[k]= vec_l[i];
25             i++;
26             k++;
27         }
28 
29         while (j<n2)
30         {
31             arr[k] = vec_r[j];
32             j++;
33             k++;
34         }
35     
36 
37 }
38 
39 void mergeSort(int arr[], int l, int r)
40 {
41     if (l < r)
42     {
43         int m = l + (r - l) / 2;
44 
45         mergeSort(arr, l, m);
46         mergeSort(arr, m + 1, r);
47 
48         merge(arr, l, m, r);
49     }
50 }