堆排序

优先队列可以用以O(NlogN)时间进行排序，基于该思想的算法叫做堆排序。它给出我们至今所见到的最佳的大O运行时间。

编码实现如下：

#include <iostream>
#include <vector>

using namespace std;

template <typename Comparable>
void heapsort( vector<Comparable> &a )
{
    for ( int i = a.size() / 2 ; i >= 0 ; i-- )         //buildHeap
        percDown( a,i,a.size() );

    for ( int j = a.size() - 1 ; j > 0 ; j-- ){         //deleteMax
        swap( a[0],a[j] );
        percDown( a,0,j );
    }
}

inline int leftChild( int i )
{
    return 2 * i;
}

template <typename Comparable>
void percDown( vector<Comparable> &a,int i,int n )      //进行下滤
{
    int child;
    Comparable tmp;

    for ( tmp = a[i] ; leftChild(i) < n ; i = child ){
        child = leftChild( i );
        if ( child != n - 1 && a[child] < a[ child + 1 ] )
            child++;
        if ( tmp < a[child] )
            a[i] = a[child];
        else
            break;
    }
    a[i] = tmp;
}

int main()
{
    cout << "请输入一些数据：" << endl;

    vector<int> vec;
    int temp;

    while ( cin >> temp )
        vec.push_back( temp );

    heapsort( vec );

    cout << "按降序排列过的数据如下：" << endl;

    vector<int>::iterator iter = vec.begin();
    while( iter != vec.end() )
        cout << *iter++ << endl;

    return 0;
}