快速排序另一种实现

#include <iostream>
using namespace std;

void print_r(int *a, int length)
{
	for (int i = 0; i < length; ++i)
	cout << a[i] << ' ';
	cout << endl;
}

void q_sort(int *a, int length)
{
	if (length == 1) {
		return ;
	}

	if (length == 2) {
		if (a[0] > a[1])
			swap(a[0], a[1]);
		return ;
	}

	int *divide = a + length - 1;
	int *less = a;
	int *greater = a + length - 2;

	while (less < a + length && greater >= a) {
		if (less < greater && *less <= *divide) {
			++less;
		} else if (greater > less && *greater > *divide) {
			--greater;
		} else {
			swap(*less, *greater);
		}

		if (less == greater) {
			if (*less <= *divide) {
				swap(*(less + 1), *divide);
			} else {
				swap(*less, *divide);
			}
			break;
		}
	}

	q_sort(a, less - a + 1);
	q_sort(less + 1, length - (less - a) - 1); 
}

int main()
{
	int a[13] = {1, 3, 2, 0, 4, 6, 8, 7, 9, 5, 13, 10, 9};
	q_sort(a, 13);
	print_r(a, 13);
}