复杂度n求数组的第K大值

利用快速排序的方法进行：

#include<iostream>
using namespace std;
int test()
{
    int a = 98;
    return a;
}

int quickSort(int* inputArray, const int left, const int right, int bigCount, int &result)
{
    cout << endl;
    cout << "right is: " << right << endl;
    cout << "left is: " << left << endl;
    if(left > right)
    {
        cout << "return -1~~~" << endl;
        result = -1;
        return -1;
    }
    //在某一次递归中，如果传入的左右两边相等，且要找第一大的数，那么就返回该值即可 
    if(left == right && bigCount == 1)
    {
        int tmp =  inputArray[right];
        cout << "inputArray[right] is: " << tmp << endl;
        result = tmp;
        return tmp;
    }
    int maxNum = 0; 
    int i = left;
    int j = right + 1;//因为下面有个j--，为了能直接用，将这里的j加1，因此输入数组最后需要填充一个数 

    int pivot = inputArray[left];
    //这里的循环进行一次遍历，在遍历的过程中，将左边大于pivot的元素以及右边小于pivot的元素进行交换，一次遍历之后，i与j相遇，此时再将pivot与j相互交换
    //那么，此时处在pivot的左边的数都是小于pivot的，pivot处在右边的数都是大于pivot的
    //这时候假设左边有m个数，右边有n个数，那么pivot就是第m+1小的数，倒数第n+1大的数
    //假设要求第k大的数，只需要右边的个数为k-1即可 
    do
    {
        do i++; while(inputArray[i] < pivot);
        do j--; while(inputArray[j] > pivot);
        if(i < j)
            swap(inputArray[i], inputArray[j]);
    }
    while(i < j);
    swap(inputArray[j], inputArray[left]);
    cout << endl << "================after one swap==================" << endl;
    for(int i = 0; i < 10; i++)
    {
        cout << inputArray[i] << " ";
    }
    cout << endl;
    int len = right - j + 1;    
    cout << "j is: " << j << endl;
    cout << "bigCount is: " << bigCount << endl;
    cout << "len is: " << len << endl;
    if(len < bigCount)//需要在左边继续寻找 
    {
        int tmp = quickSort(inputArray ,left, j - 1, bigCount - len, result);
        if(tmp != -1)
            return tmp;
    }
    else if(len > bigCount) //需要在右边继续寻找
    {
        int tmp = quickSort(inputArray, j + 1, right, bigCount, result);
        if(tmp != -1)
            return tmp;
    }
    else
    {
        int tmp =  inputArray[j];
        cout << "inputArray[j] is: " << tmp << endl;
        result = tmp;
        return tmp;
    }     
}
int main()
{
    int a[] = {8, 6, 4, 2, 0, 1, 3, 5, 7, 9, 99};
    cout << endl << "================origion==================" << endl;
    for(int i = 0; i < 10; i++)
    {
        cout << a[i] << " ";
    }
    int rrrr = 0;
    int result = 0;
    cout<<endl;
    result = quickSort(a, 0, 9, 4, rrrr);
    cout<<endl<<endl;
    cout << "rrrr is " << rrrr << endl;
    cout << "result is " << result << endl;
    cout<<endl<<endl;
    cout << endl << "================result==================" << endl;
    for(int i = 0; i < 10; i++)
    {
        cout << a[i] << " ";
    }
    return 0;
}