快排

#include <iostream>

using namespace std;
void swap(int & a, int & b)
{
    int temp = 0;
    temp = a;
    a = b;
    b = temp;
    return;
}
 int partition(int data[], int start, int end)
 {
     if (data == nullptr)
     {
         throw exception("invalid input");
     }
     
     int small = start - 1;
     int mid = data[start];	//设置哨兵，可随意选取，此处可优化，避免选取最后一个或最前一个，尽量选取中部
     for (int i = start; i < end; i++)
     {
        if (data[i] < mid)	//<和<=都可以
        {
            small++;	//此处判断small和i可省略一次交换，例如第一个参数就小于mid的情况下
            swap(data[small], data[i]);
        }
     }

     small++;
     swap(data[small], mid);
     return small;
 }
 void quick_sort(int data[], int start, int end)
 {
     if (start == end)
     {
         return;
     }

     int mid = partition(data, start, end);
     quick_sort(data, start, mid - 1);
     quick_sort(data, mid + 1, end);
 }

方法二

	int partition2(int a[], int p, int r)
	{
		int key = a[p];

		while (p < r)
		{
			while (p < r && a[r] > key)
			{
				r--;
			}

			if (p < r)
			{
				a[p] = a[r];
			}

			while (p < r && a[p] < key)
			{
				p++;
			}

			if (p < r)
			{
				a[r] = a[p];
			}
		}

		a[r] = key;
		return r;
	}
	void quick_sort2(int a[], int p, int r)
	{
		int middle;

		if (p < r)
		{
			middle = partition2(a, p, r);
			quick_sort2(a, p, middle - 1);
			quick_sort2(a, middle + 1, r);
		}
	}
};

int main()
{
	Solution s;
	s.cplus_solution();
	return 0;
}