算法導論第6章代碼之堆排序

算法：

// 對第i個節點構建最大堆
void build_max_heap(int *a, int i, int n)
{
    int max = i;
    int left = 2 * i + 1;
    int right = 2 * i + 2;
                    
    if (left < n && a[left] > a[max]) {
        max = left;
    }
                    
    if (right < n && a[right] > a[max]) {
        max = right;
    }
                    
    if (i != max) {
                        
        int temp = a[i];
        a[i] = a[max];
        a[max] = temp;
                        
        build_max_heap(a, max, n);
                        
    }
                    
}
void HeapSort(int *a, int n)
{
    int i;
    for (i = n / 2; i >= 0; i--) {
        build_max_heap(a, i, n);
    }
                    
    for (i = n - 1; i > 0; i--) {
                        
        int temp = a[i];
        a[i] = a[0];
        a[0] = temp;
                        
        build_max_heap(a, 0, i);
    }
                    
}
int main(int argc, const char * argv[])
{
    int a[] = {3, 5, 1, 2, 5, 4};
    int n = sizeof(a) / sizeof(*a);
                    
    HeapSort(a, n);
                    
    int i = 0;
    for (; i < n; i++) {
        printf("%d ", a[i]);
    }
                    
    return 0;
}

輸出：1 2 3 4 5 5