堆排序交换和比较。如何通过两个函数传递它们

Question

我正在尝试计算 C++ 中堆排序算法的交换和比较。到目前为止，我已经编写了主要函数和两个方法（都是堆排序算法）。

int main()
{
    int countComp = 0, countSwap = 0;
    int arr[] = {12, 11, 13, 5, 6, 7};
    int n = sizeof(arr)/sizeof(arr[0]);

    heapSort(arr, n, countComp, countSwap);

    cout << "Sorted array is \n";
    printArray(arr, n);

    cout << "comparisons: " << countComp <<  " swaps: " << countSwap << endl;
}

我知道我犯了某种逻辑错误，因为通过参数传递变量然后用递归调用这些函数对我来说非常混乱。

void heapify(int arr[], int n, int i, int& countComparisons, int& countSwaps)
{
    int largest = i;  // Initialize largest as root
    int l = 2*i + 1;  // left = 2*i + 1
    int r = 2*i + 2;  // right = 2*i + 2

    // If left child is larger than root
    if (l < n && arr[l] > arr[largest])
    {
        countComparisons++;
        largest = l;
    }

    // If right child is larger than largest so far
    if (r < n && arr[r] > arr[largest])
    {
        countComparisons++;
        largest = r;
    }

    // If largest is not root
    if (largest != i)
    {
        countSwaps++;
        swap(arr[i], arr[largest]);

        // Recursively heapify the affected sub-tree
        heapify(arr, n, largest, countComparisons, countSwaps);
    }
}

// main function to do heap sort
void heapSort(int arr[], int n, int& countComparisons, int& countSwaps)
{
    // Build heap (rearrange array)
    for (int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i, countComparisons, countSwaps);

    // One by one extract an element from heap
    for (int i=n-1; i>=0; i--)
    {
        countSwaps++;
        // Move current root to end
        swap(arr[0], arr[i]);

        // call max heapify on the reduced heap
        heapify(arr, n, 0, countComparisons, countSwaps);
    }
}

我很确定错误与通过引用传递的参数有关。有人可以纠正我吗？我被这个问题困住了。或者也许有更好的方法来计算交换和比较？

如果我运行这个，我得到答案： 比较：12 互换：16

Answer 1

Sorted array is
13, 12, 11, 5, 7, 6,
comparisons: 12 swaps: 16

您在 heapSort 中有一个错误导致了错误的排序结果。它还会导致成功排序失败的比较和交换次数增加。在对 heapify

的第二次调用中将 n 更改为 i

void heapSort(int arr[], int n, int& countComparisons, int& countSwaps)
{
    for(int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i, countComparisons, countSwaps);

    for(int i = n - 1; i >= 0; i--)
    {
        countSwaps++;
        swap(arr[0], arr[i]);
        //heapify(arr, n, 0, countComparisons, countSwaps);
        heapify(arr, i, 0, countComparisons, countSwaps); //<=== changed `n` to `i`
    }
}

结果：

Sorted array is
5, 6, 7, 11, 12, 13,
comparisons: 7 swaps: 11

Test on ideone

堆排序交换和比较。如何通过两个函数传递它们

Heapsort swap and comparisons. How to pass them through two functions

c++

sorting

heapsort