最大k个数，以及类模板

#include <iostream>
using namespace std;

template<class T>
class CTopK
{
public:
    CTopK();
    ~CTopK();
    T*  m_Data;
    int GetTopK(const char* sFile, int& nTop);
private:
    void Clear();
    void HeapAdjust(int nStart, int nLen);
    void BuildHeap(int nLen);
};

template<class T>
CTopK<T>::CTopK()
{
    m_Data = NULL;
}

template<class T>
CTopK<T>::~CTopK()
{
    Clear();
}

template<class T>
void CTopK<T>::Clear()
{
    if (NULL != m_Data)
    {
        delete[] m_Data;
        m_Data = NULL;
    }
}

//获取前top的k个数
template<class T>
int CTopK<T>::GetTopK(const char* sFile, int& nTop)
{
    FILE* fp = NULL;
    T fData;
    int i = 0;

    //判断输入参数
    if ( (NULL == sFile) || (nTop <= 0) )
    {
        cout << "error parameter" << endl;
        return -1;
    }

    //清除操作
    Clear();

    //打开文件
    fp = fopen(sFile, "r");
    if (NULL == fp)
    {
        cout << "open file failed!" << endl;
        return -1;
    }

    //分配空间
    m_Data = new T[nTop];
    if (NULL == m_Data)
    {
        cout << "new operator failed!" << endl;
        return -1;
    }

    cout << "please wait..." << endl;

    //读取前nTop个数据,注意数据的类型T
    for (i = 0; i < nTop; i++)
    {
        if (EOF != fscanf(fp, "%d", &fData))
        {
            m_Data[i] = fData;
        }
        else
        {
            break;
        }
    }

    //最大的个数小于nTop,求前i个数据
    if (i < nTop)
    {
        nTop = i;
    }
    else
    {
        BuildHeap(nTop);//建立小顶堆

        while (EOF != fscanf(fp, "%d", &fData))
        {
            if (fData > m_Data[0])
            {
                //交换并调整堆
                m_Data[0] = fData;
                HeapAdjust(0, nTop);
            }
        }
    }

    return 0;
}

//调整小根堆，堆顶为Top K最小
template<class T>
void CTopK<T>::HeapAdjust(int nStart, int nLen)
{
    int nMinChild = 0;
    T fTemp;

    while ( ( 2 * nStart + 1) < nLen)
    {
        nMinChild = 2 * nStart + 1;
        if ( (2 * nStart + 2) < nLen)
        {
            //比较左子树和右子树,记录最小值的Index
            if (m_Data[2 * nStart + 2] < m_Data[2 * nStart + 1])
            {
                nMinChild = 2 * nStart + 2;
            }
        }

        //change data
        if (m_Data[nStart] > m_Data[nMinChild])
        {
            //交换nStart与nMaxChild的数据
            fTemp = m_Data[nStart];
            m_Data[nStart] = m_Data[nMinChild];
            m_Data[nMinChild] = fTemp;

            //堆被破坏,需要重新调整
            nStart = nMinChild;
        }
        else
        {
            //比较左右孩子均大则堆未破坏,不再需要调整
            break;
        }
    }
}

//建立堆
template<class T>
void CTopK<T>::BuildHeap(int nLen)
{
    int i = 0;
    T nTemp;

    //将m_Data[0, Len-1]建成小根堆，这里只维护一个小根堆，不排序
    for (i = nLen / 2  - 1; i >= 0; i--)
    {
        HeapAdjust(i, nLen);
    }
}

int main(int argc, char* argv[])
{
    char   szFile[100] = {0};
    int     nNum = 0;
    CTopK<int> objTopSum;

    cout << "please input count file name:" << endl;
    cin >> szFile;
    cout << "please input top num:"<< endl;
    cin >> nNum;
    objTopSum.GetTopK(szFile, nNum);

    int fSum = 0;
    for (int i = 0; i < nNum; i++)
    {
        cout<<objTopSum.m_Data[i]<<" ";
        fSum += objTopSum.m_Data[i];
    }
    cout << "
top " << nNum << " value = " << fSum << endl;

    return 0;
}