堆

还记得是大二的时候写过堆，没想到今天写的时候一气呵成

#include <stdio.h>

#ifdef __cplusplus
extern "C" {
#endif

#define PARENT_INDEX(i) (((i) - (!((i) & 1))) / 2)
#define LSON_INDEX(i) ((i) * 2 + 1)
#define RSON_INDEX(i) ((i) * 2 + 2)

#define SWAP(a, b) do{\
	a = a ^ b;\
	b = a ^ b;\
	a = a ^ b;\
}while(0)
	

struct heap_t{
	int * ptr_buf;
	int size;	  /* 以4字节为单位 */
	int capacity; /* 以4字节为单位 */
};

void heap_shift_up(struct heap_t * heap, int index)
{
	if(heap->size > heap->capacity || index >= heap->size)
		return;

	while(index != 0)
	{
		if(heap->ptr_buf[index] > heap->ptr_buf[PARENT_INDEX(index)])
			break;

		/* 交换当前节点和父节点的值 */
		SWAP(heap->ptr_buf[index], heap->ptr_buf[PARENT_INDEX(index)]);		
		index = PARENT_INDEX(index);	
	}
}

void heap_shift_down(struct heap_t * heap, int index)
{
	int smaller_son_index;

	if(heap->size > heap->capacity || index >= heap->size)
		return;	

	while(LSON_INDEX(index) <= heap->size)
	{
		/* 找出左儿子和右儿子中较小的一个的索引 */
		smaller_son_index = LSON_INDEX(index);
		if(heap->ptr_buf[RSON_INDEX(index)] < heap->ptr_buf[LSON_INDEX(index)]
			&& RSON_INDEX(index) <= heap->size)
			smaller_son_index = RSON_INDEX(index);

		/* 如果当前节点小于左右儿子，则成功 */
		if(heap->ptr_buf[index] < heap->ptr_buf[smaller_son_index])
			break;

		/* 交换当前节点和较小的儿子的值 */
		SWAP(heap->ptr_buf[smaller_son_index], heap->ptr_buf[index]);		
		index = smaller_son_index;
	}
}

/* 初始化堆 */
void make_heap(struct heap_t * heap)
{
	int i = 0;

	if(heap->size > heap->capacity)
		return;	
	
	for(i = heap->size - 1; i >= 0; i--)
		heap_shift_down(heap, i);
}


void remove_from_heap(struct heap_t * heap, int index)
{
	if(heap->size > heap->capacity || index >= heap->size)
		return;	

	/* 将最后一个元素与需要移除的元素交换 */
	SWAP(heap->ptr_buf[index], heap->ptr_buf[heap->size - 1]);
	heap->size--;

	/* 重新调整堆 */
	heap_shift_up(heap, index);
	heap_shift_down(heap, index);
}

/* 向堆中添加元素 */
bool add_to_heap(struct heap_t * heap, int val)
{
	if(heap->size + 1 > heap->capacity)
		return false;

	heap->ptr_buf[heap->size] = val;
	heap->size++;

	heap_shift_up(heap, heap->size - 1);
}

int
main(int c, char **v) {
	int i;
	struct heap_t heap;
	int arr[20] = {1, 20, 2, 30, 30, 4, 4, 100, 100, 100, 100, 5, 5, 6, 6};

	heap.size = 15;
	heap.capacity = 20;
	heap.ptr_buf = arr;

	make_heap(&heap);

	remove_from_heap(&heap, 4);

	add_to_heap(&heap, -1);

	for(i = 0; i < heap.size; i++)
		printf("%d\n", arr[i]);
	printf("size: %d\n", heap.size);		

	return 0;
}

#ifdef __cplusplus
}
#endif