快速排序总结

1. 随机数做Pivot

#include <iostream>
#include <ctime>

void swap(int* a, int* b)
{
	if (a == b)
		return;

	*a = *a ^ *b;
	*b = *a ^ *b;
	*a = *a ^ *b;
};

int partition(int* a, int left, int right)
{
	srand(time(NULL));
	int pivot = rand() % (right - left + 1) + left;

	swap(&a[pivot], &a[right]);

	int front = left;
	int curIdx = left;

	while (curIdx < right)
	{
		if (a[curIdx] < a[right])		
			swap(&a[curIdx], &a[front++]);
		
		curIdx++;
	}

	swap(&a[front], &a[right]);
	return front;
};

void quickSort(int* a, int left, int right)
{
	if (left < right)
	{
		int pivot = partition(a, left, right);
		quickSort(a, left, pivot - 1);
		quickSort(a, pivot + 1, right);
	}
};

int main()
{
	int a[10] = {10, 9, 8, 7, 6, 55, 11, 5, 3, 2};

	quickSort(a, 0, sizeof(a) / sizeof(int) - 1);
	return 0;
}

2. left, mid, right的中位数做pivot

#include <iostream>
#include <ctime>

void swap(int* a, int* b)
{
	if (a == b)
		return;

	*a = *a ^ *b;
	*b = *a ^ *b;
	*a = *a ^ *b;
};

int partition(int* a, int left, int right)
{	
	int pivot = (left + right) / 2;

	//Median from 3 numbers
	if (a[left] > a[pivot])
		swap(&a[left], &a[pivot]);
	if (a[left] > a[right])
		swap(&a[left], &a[right]);
	if (a[pivot] > a[right])
		swap(&a[pivot], &a[right]);

	swap(&a[pivot], &a[right]);

	int front = left;
	int curIdx = left;

	while (curIdx < right)
	{
		if (a[curIdx] < a[right])		
			swap(&a[curIdx], &a[front++]);
		
		curIdx++;
	}

	swap(&a[front], &a[right]);
	return front;
};

void quickSort(int* a, int left, int right)
{
	if (left < right)
	{
		int pivot = partition(a, left, right);
		quickSort(a, left, pivot - 1);
		quickSort(a, pivot + 1, right);
	}
};

int main()
{
	int a[10] = {10, 9, 8, 7, 6, 55, 11, 5, 3, 2};

	quickSort(a, 0, sizeof(a) / sizeof(int) - 1);
	return 0;
}