排序

 

快速排序quickSort

#include <iostream>
#include <vector>
using namespace std;

int findPivot(vector<int> &a, int lo, int hi)
{
	int ce = (lo + hi) / 2;
	if (a[lo] > a[ce])
		swap(a[lo], a[ce]);
	if (a[lo] > a[hi])
		swap(a[lo], a[hi]);
	if (a[ce] > a[hi])
		swap(a[ce], a[hi]);

	swap(a[ce], a[hi - 1]);
	return a[hi-1];
}

void qSort(vector<int> &a, int lo, int hi)
{
	if (hi <= lo)
		return;
	if (hi - lo == 1)
	{
		if(a[lo]>a[hi])
			swap(a[lo], a[hi]); 
		return;
	}

	int pivot = findPivot(a, lo, hi);
	int i = lo, j = hi-1; //注意j取值
	while (1)
	{
		while (a[++i] < pivot);
		while (a[--j] > pivot);
		if (i < j)
			swap(a[i], a[j]);
		else
			break;
	}
	swap(a[i], a[hi - 1]);//还原pivot
	qSort(a, lo, i - 1);
	qSort(a, i + 1, hi);
}

void quickSort(vector<int> &a)
{
	qSort(a, 0, a.size() - 1);
}

int main()
{
	vector<int> a{ 10, 2, 3, 7, 1, 6, 4, 9, 2 };
	quickSort(a);

	for (auto &ele : a)
		cout << ele << " ";

    return 0;
}