归并排序

 1 #include <iostream>
 2 #include <cstring>
 3 using namespace std;
 4 
 5 void merge(int *a, int p, int q, int r) {
 6     int n1 = q - p + 1;
 7     int n2 = r - q;
 8     int *L = new int[n1];
 9     int *R = new int[n2];
10     for (int i = 0; i < n1; i++)
11         L[i] = a[p + i];
12     for (int i = 0; i < n2; i++)
13         R[i] = a[q + 1 + i];
14     int key = p;
15     int i = 0, j = 0;
16     while (i < n1 || j < n2) {
17         if (i < n1&&j < n2)
18             if (L[i] < R[j]) a[key++] = L[i++];
19             else a[key++] = R[j++];
20         else
21             if (i < n1) a[key++] = L[i++];
22             else a[key++] = R[j++];
23     }
24         delete[] L;
25         delete[] R;
26         return;
27     }
28 
29 void mergeSort(int *a, int l, int r) {
30     if (l < r) {
31         int m = (l + r) / 2;
32         mergeSort(a, l, m);
33         mergeSort(a, m + 1, r);
34         merge(a, l, m, r);
35     }
36     return;
37 }
38 
39 
40 int main() {
41     int a[100];
42     int n;
43     while (cin>>n)
44     {
45         for (int i = 0; i < n; i++)
46             cin >> a[i];
47 
48         mergeSort(a, 0, n - 1);
49 
50         for (int i = 0; i < n; i++)
51             cout << a[i] << " ";
52         cout << endl;
53     }
54 }