快排

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void shuffle(vector<int> &nums)
{
	int n = nums.size();
	for (int i = 0; i < n; i++)
	{
		swap(nums[i], nums[rand() % (n - i) + i]);
	}
	return;
}

int partition(vector<int> &nums, int lo, int hi)
{
	swap(nums[lo], nums[rand() % (hi - lo + 1) + lo]);
	int pivot = nums[lo];
	while (lo < hi)
	{
		while (lo < hi && pivot <= nums[hi])
			hi--;
		nums[lo] = nums[hi];
		while (lo < hi&&nums[lo] <= pivot)
			lo++;
		nums[hi] = nums[lo];
	}
	nums[lo] = pivot;
	return lo;
}
int partition2(vector<int> &nums, int lo, int hi)
{
	swap(nums[lo], nums[rand() % (hi - lo + 1) + lo]);
	int pivot = nums[lo];
	while (lo < hi)
	{
		while (lo < hi)
		{
			if (pivot < nums[hi])
				hi--;
			else
			{
				nums[lo++] = nums[hi];
				break;
			}
		}
		while (lo < hi)
		{
			if (nums[lo] < pivot)
				lo++;
			else
			{
				nums[hi--] = nums[lo];
				break;
			}
		}
	}
	nums[lo] = pivot;
	return lo;
}


void quickSort(vector<int> &nums, int lo, int hi)
{
	if (hi - lo < 2) return;
	int mid = partition2(nums, lo, hi - 1);
	//int mid = partition(nums, lo, hi - 1);
	quickSort(nums, lo, mid);
	quickSort(nums, mid + 1, hi);
	return;
}

int main()
{
	vector<int> a;
	for (int i = 0; i < 20; i++)
		a.push_back(i);
	for (int i = 5; i < 10; i++)
		a[i] = 3;
	shuffle(a);
	cout << "shuffle a: " << endl;
	for (auto &i : a) cout << i << " ";
	cout << endl;
	vector<int> b(a);
	quickSort(b, 0, b.size());
	cout << "quickSort b: " << endl;
	for (auto &i : b) cout << i << " ";
	cout << endl;

}