排序算法（二）

堆排序
//7-heap sort method
void build_heap( int *arr, int start, int n )
{
        if( (start+1)*2 > n )
                return;
        if( (start+1)*2 == n )
        {
                if( arr[start] < arr[(start+1)*2-1] )
                {
                        int tmp;
                        tmp = arr[start];
                        arr[start]=arr[(start+1)*2-1];
                        arr[(start+1)*2-1]=tmp;
                }
        }
        else
        {
                int tmp;
                if( arr[start] < arr[(start+1)*2-1] )
                {
                        tmp = arr[start];
                        arr[start] = arr[(start+1)*2-1];
                        arr[(start+1)*2-1] = tmp;
                        build_heap( arr, (start+1)*2-1, n );
                }
                if( arr[start] < arr[(start+1)*2] )
                {
                        tmp = arr[start];
                        arr[start] = arr[(start+1)*2];
                        arr[(start+1)*2] = tmp;
                        build_heap( arr, (start+1)*2, n );
                }
        }
}
void init_heap( int *arr, int n )
{
        int offset;

        if( n%2==0 )
        {
                if( arr[n/2-1] < arr[n-1] )
                {
                        int tmp = arr[n/2-1];
                        arr[n/2-1]=arr[n-1];
                        arr[n-1]=tmp;
                }
                offset = n-1;
        }
        else
                offset = n;
        for( ; offset>1; offset-=2 )
        {
                if( arr[offset/2-1] < arr[offset-1] )
                {
                        int tmp;
                        tmp = arr[offset/2-1];
                        arr[offset/2-1]=arr[offset-1];
                        arr[offset-1]=tmp;
                        build_heap(arr,offset-1, n );
                }

                if( arr[offset/2-1] < arr[offset-2] )
                {
                        int tmp;
                        tmp = arr[offset/2-1];
                        arr[offset/2-1]=arr[offset-2];
                        arr[offset-2]=tmp;
                        build_heap(arr,offset-2, n );
                }
        }
}
void heap_sort( int *arr, int n )
{
        int offset=n;
        init_heap( arr, n );
        for( ; offset>1; )
        {
                --offset;
                int tmp=arr[offset];
                arr[offset]=arr[0];
                arr[0]=tmp;
                build_heap( arr, 0, offset );
        }
}