堆排序

 1 template<typename T>
 2 void percolatedown(T a[], int n, int i)
 3 {
 4     T tm = a[i];
 5     int child = i<<1;
 6     for (; child <= n-1; i=child, child=(child<<1)) {
 7         //choose the little child
 8         if (child!= n-1 && a[child] > a[child+1])
 9             child++;
10         if (tm > a[child])
11             a[i] = a[child];
12         else
13             break;
14     }
15     a[i] = tm;
16 }
17 
18 template<typename T>
19 void heapsort(T a[], int n)
20 {
21     for (int i=n/2; i>=0; --i)
22         percolatedown(a,n,i);
23     for (int j=n-1; j>=0; --j) {
24         T min = a[0];
25         a[0] = a[j];    //delete the minimal value
26         a[j] = min;
27         percolatedown(a,j,0);
28     }
29 
30     reverse(a,n);
31 }
32 
33 template<typename T>
34 void reverse(T a[], int n)
35 {
36     for (int i=0; i!=n/2; ++i) {
37         T tm = a[i];
38         a[i] = a[n-1-i];
39         a[n-1-i] = tm;
40     }
41 }