关于快速排序参考之前的文章：https://blog.csdn.net/hpu2022/article/details/83069041

关于二分查找的参考之前的文章：https://blog.csdn.net/hpu2022/article/details/79845630

code:

#include <iostream>
using namespace std;

int BinarySearch(int *a , int low, int high, int key)
{
    if(low > high)
        return -1;
    int mid = (low + high) / 2;
    if(key == a[mid])
        return mid;
    else if(key < a[mid])
        return BinarySearch(a, low, mid-1, key);
    else 
        return  BinarySearch(a, mid+1, high, key);
    
}
void QuickSort(int *a, int L, int R)
{
    if(L < R)
    {
        int i = L;
        int j = R;
        int num = a[L];
        while(i < j)
        {
            while(i < j && a[j] >= num)
                --j;
            if(i < j)
                a[i++] = a[j];
            while(i < j && a[i] < num)
                ++i;
            if(i < j)
                a[j--] = a[i];
        }
        a[i] = num;
        QuickSort(a, L, i-1);
        QuickSort(a, i+1, R);
    }
}

int main()
{
    int a[100];
    for(int i=0; i<6; i++)
        cin >> a[i];
    QuickSort(a, 0, 5);
    int number;
    cin >> number;
    int index = BinarySearch(a, 0, 5, number);
    if(index != -1)
        cout << a[index] << endl;
    else
        cout << "-1" << endl;
    



    return 0;
}