堆排序 heapsort

#include <iostream>

  

using namespace std;

void heapify(int arr[], int n, int i)

{

    int largest = i; 

    int l = 2*i + 1; 

    int r = 2*i + 2; 

  

    

    if (l < n && arr[l] > arr[largest])

        largest = l;

  

    

    if (r < n && arr[r] > arr[largest])

        largest = r;

  

 

    if (largest != i)

    {

        swap(arr[i], arr[largest]);

  

        //向下遞歸

        heapify(arr, n, largest);

    }

}

  

 

void heapSort(int arr[], int n)

{

    // Build heap (rearrange array)

    for (int i = n / 2 - 1; i >= 0; i--)

        heapify(arr, n, i);

  

    for (int i=n-1; i>=0; i--)

    {

       

        swap(arr[0], arr[i]);

  

        // call max heapify on the reduced heap

        heapify(arr, i, 0);

    }

}

void printArray(int arr[], int n)

{

    for (int i=0; i<n; ++i)

        cout << arr[i] << " ";

    cout << "\n";

}

int main()

{

    int arr[] = {12, 11, 13, 5, 6, 7};

    int n = sizeof(arr)/sizeof(arr[0]);

  

    heapSort(arr, n);

  

    cout << "Sorted array is \n";

    printArray(arr, n);

}