将值插入最大二进制堆时出现问题

Question

我使用 C 创建了一个二进制堆。这里是初始化堆和插入值的函数

int *heapArray; // pointer to array of elements in heap
int capacity = 0; // maximum possible size of min heap, initially set to 0
int heap_size; // Current number of elements in min heap
int d = 2;  //max number of children per node

int getParent(int i) //get the parent index of i
{
    return (i/d);
}

bool isFull() //check if heap is full
{
    if(heap_size == capacity)
        return true;
    if(heap_size < capacity)
        return false;
}

void initializeHeap(int cap) //initialize the heap
{
    heap_size = 0;
    capacity = cap;
    heapArray = (int*)malloc(cap*sizeof(int));
}

void insertValue(int x) //insert a value into the heap
{
    if(isFull()) //If heap is already full, double the heap size
    {
        capacity = 2*capacity;
        heapArray = realloc(heapArray,capacity*sizeof(int));
    }

    heap_size = heap_size + 1;
    heapArray[heap_size] = x; //insert new value into heap (not zero-indexed)
    maxHeapSwim(heap_size);
}

void maxHeapSwim(int k) //move value up the heap to maintain max-heap order
{
    while(k > 1 && heapArray[getParent(k)] < heapArray[k])
    {
        swap(&heapArray[k],&heapArray[parent(k)]);
        k = parent(k);
    }
}

然后在 main() 方法中，我尝试将值插入到堆中并打印出值：

int main()
{

  initializeHeap(1); //Set the heap capacity to 1

  insertValue(2);
  insertValue(3);
  insertValue(1);
  insertValue(6);
  insertValue(4);

  printf("\n");
  printf("%i", heapArray[1]);
  printf("\n");
  printf("%i", heapArray[2]);
  printf("\n");
  printf("%i", heapArray[3]);
  printf("\n");
  printf("%i", heapArray[4]);
  printf("\n");
  printf("%i", heapArray[5]);
  printf("\n");

  return 0;

}

由于这是一个最大堆，我希望输出如下所示：

6
4
1
2
3

但是，它看起来像这样：

6
4
1
0
3

我不明白。为什么2变成0？我觉得这与我如何将 insertValue() 函数中的堆大小加倍有关....可能是我使用 realloc 的方式。是不是我做错了什么？

要注意的另一件事是我的二进制堆不是零索引的。第一个值插入 heapArray[1]，第二个值插入 heapArray[2]，以此类推。

Answer 1

您的代码第一部分的一些更改对我有用。

实现swap() 和一些小改动。

代码

#define false 0
#define true 1

int *heapArray; // pointer to array of elements in heap
int capacity = 0; // maximum possible size of min heap, initially set to 0
int heap_size; // Current number of elements in min heap
int d = 2;  //max number of children per node

int getParent(int i) //get the parent index of i
{
    return (i/d);
}

void maxHeapSwim(int k) //move value up the heap to maintain max-heap order
{
    while(k > 1 && heapArray[getParent(k)] < heapArray[k])
    {
        //swap(&heapArray[k],&heapArray[parent(k)]);
        int x=heapArray[k];
        heapArray[k]=heapArray[getParent(k)];
        heapArray[getParent(k)]=x;
        k = getParent(k);
    }
}

int  isFull() //check if heap is full
{
    if(heap_size == capacity)
        return true;
    if(heap_size < capacity)
        return false;
}

void initializeHeap(int cap) //initialize the heap
{
    heap_size = 0;
    capacity = cap;
    heapArray = (int*)malloc(cap*sizeof(int));
}

void insertValue(int x) //insert a value into the heap
{
    if(isFull()) //If heap is already full, double the heap size
    {
        capacity = 2*capacity;
        heapArray = realloc(heapArray,capacity*sizeof(int));
    }

    heap_size = heap_size + 1;
    heapArray[heap_size] = x; //insert new value into heap (not zero-indexed)
    maxHeapSwim(heap_size);
}




int main()
{  

  initializeHeap(1); //Set the heap capacity to 1

  insertValue(2);
  insertValue(3);
  insertValue(1);
  insertValue(6);
  insertValue(4);

  printf("\n");
  printf("%i", heapArray[1]);
  printf("\n");
  printf("%i", heapArray[2]);
  printf("\n");
  printf("%i", heapArray[3]);
  printf("\n");
  printf("%i", heapArray[4]);
  printf("\n");
  printf("%i", heapArray[5]);
  printf("\n");

  return 0;
}

输出

./code 


6
4
1
2
3

Answer 2

这对我有用：

void insertValue(int x)
{
    if(capacity < 10)
    {
        capacity = 10;
        heapArray = (int*)realloc(heapArray,capacity*sizeof(int));
    }
    if(heap_size >= capacity/2)
    {
        capacity += 10;
        heapArray = (int*)realloc(heapArray,capacity*sizeof(int));
    }

    heap_size = heap_size + 1;
    heapArray[heap_size] = x;
    maxHeapSwim(heap_size);
}

关键是要确保二进制堆永远不会满。